First-onset of obsessive-compulsive disorder immediately after delivery in primiparous women may be associated with later development of bipolar disorder. Clinicians providing care to these women should assess them routinely for obsessions and compulsions as well as emerging symptoms of mania. The role of antidepressants in the triggering of mania is unclear. Ms. C, a 32-year-old healthy female, developed obsessive thoughts and images of harm coming to the newborn within a month of her first delivery, 7 years earlier. She felt sad due to the disturbing nature of obsessions but did not have other symptoms of depression. Due to the persistent nature of obsessions and their impairing effect on her daily functioning, she consulted her family physician, who diagnosed her with obsessive–compulsive disorder and prescribed sertraline 50 mg a day. The obsessions and compulsions resolved within 6 months. She remained on the same dose of sertraline until her second pregnancy, when she developed an episode of major depression for the first time. As the symptoms progressed, she attempted suicide by hanging and was hospitalized for 3 weeks. During the hospital stay, the diagnoses of major depressive disorder and obsessive–compulsive disorder were confirmed. There was no evidence of hypo/mania during the hospitalization. The sertraline dose was optimized to 150 mg daily. Following her discharge from the hospital, she was referred to our perinatal clinic for follow-up care. The depression remitted a few weeks later; however, she had a recurrence of depression immediately after delivery despite the continued use of sertraline 150 mg daily. Since she could not tolerate a higher dose of sertraline, we decided to keep her on the same dose. She was invited to participate in an open trial of aripiprazole, addition to antidepressant therapy for unipolar postpartum depression at our center. Using the Structured Clinical Interview for DSM-IV, the diagnoses of obsessive–compulsive disorder and major depressive disorder were once again confirmed. She indicated that prior to her pregnancy she had had anxiety symptoms premenstrually for which she was prescribed clonazepam 0.5 mg od prn. There was no known history of psychiatric illness in the family. As part of the study protocol, she was prescribed aripiprazole 2 mg daily and was advised to continue taking sertraline 150 mg daily. Within 2 weeks of addition of aripiprazole, the depression remitted and she was free of depression over the next 2 years (Figure 1). During the follow-up, she denied symptoms of hypomania; however, we noted that her Young Mania Rating Scale (YMRS) score increased from 0 at baseline study visit to 5 (normal range 0–60) at the termination of the study. Three years later, she was referred back to us with a recent history of recurrent episodes of depression and hypomania. The diagnosis was changed to bipolar II disorder. We recommended a gradual tapering of sertraline due to the history of rapid cycling. During the taper, she developed a manic episode with mixed features and was hospitalized. During the hospital stay, both sertraline and aripiprazole were tapered off and she was treated with lithium 750 mg and quetiapine 500 mg a day. Her mood stabilized quickly; however, within 2 months following her discharge from the hospital, she had a recurrence of obsessive–compulsive disorder. The obsessive–compulsive disorder remitted following the addition of risperidone 0.5 mg a day. Risperidone was substituted with topiramate 50 mg after she had another recurrence of obsessive–compulsive disorder. Topiramate was subsequently stopped due to cognitive side effects. Over the past 5 years, she has continued to have recurrences of brief episodes of depression and mixed states as well as of obsessive–compulsive disorder. However, she has not required a psychiatric hospitalization and has remained gainfully employed. Reproductive events impact the course of obsessive–compulsive disorder in women. Approximately, 5% of women with the disorder have onset of symptoms in the postpartum period.1 A population-based study from Denmark found that women with first psychiatric contact during the first month postpartum were at high risk of developing bipolar disorder.2 Similarly, high rates of conversion to bipolar disorder among women with first onset of depression in the postpartum period were found in the Bipolar Disorders: Improving Diagnosis, Guidance and Education (BRIDGE) study.3 As far as we know, there are no reports of later onset of bipolar disorder among women with postpartum onset of obsessive–compulsive disorder. Our case adds to the accumulating evidence that first onset of psychiatric illness in the postpartum period may be a signature of bipolar disorder.2, 3 It is possible that the use of sertraline without a mood stabilizer contributed to the emergence of hypo/manic symptoms in our case.4 As far as we know, there was no known personal or family history of bipolar disorder or obsessive–compulsive disorder. As shown in Figure 1, the patient developed episodes of hypo/mania following the long-term use of sertraline. Further, it is possible that sertraline use in the context of cryptic bipolarity may have contributed to the suicide attempt in pregnancy. Our case suggests that prior to the introduction of an antidepressant, women with first-onset of obsessive–compulsive disorder in the first-month postpartum should be assessed for symptoms of hypo/mania. Similarly, there should be monitoring for symptoms of depression as well as hypo/mania during and after pregnancy. Our patient had first onset of depression during pregnancy and experienced a recurrence of depression after delivery rather than obsessive–compulsive disorder. This means that recurrence after delivery is not true to type. Mood stabilizers alone or in combination with second-generation antipsychotics should be the preferred treatment option for women with bipolar disorder and comorbid obsessive–compulsive disorder. According to the results of a systematic review lithium, in combination with aripiprazole, appeared to be the best option in patients with treatment-resistant comorbidity. Given its salient role in the triggering of both obsessive–compulsive disorder and bipolar disorder, the postpartum period should offer researchers a remarkable opportunity to study the relationship between these disorders in women.5 Dr. Al-Farayedhi reports no financial relationships with commercial interests. Dr. Sharma has received grant support from, participated on scientific advisory boards for, or served on speakers' bureaus of Assurex, Genome Canada, Neurocrine Biosciences, Sage Therapeutics, Stanley Medical Research Institute, and Sunovion Pharmaceuticals. Data sharing not applicable to this article as no data sets were generated or analysed during the current study.