BackgroundDepression is a serious mental illness that affects patients’ treatment outcome and caregiver’s day to day life. The prevalence of depression among caregivers of patients with severe mental illness is greater than the general population. Little is known about depression among primary caregivers of patients with severe mental illness in Ethiopia. This study is aimed at assessing prevalence of depression and associated factors among primary caregivers of patients with mental illness.MethodsA cross-sectional study was conducted among primary caregivers of patients with severe mental illness in Jimma University Teaching Hospital. Patient health questionnaire (PHQ-9) was used to assess depression. A multidimensional scale of perceived social support (MSPSS) was used to assess perceived social support; Cut down, Annoyed, Guilty, Eye opener (CAGE) scale was used to assess alcohol use disorder. After conducting descriptive analyses, logistic regression analysis was finally used for bivariate and multivariable analysis.ResultThe overall prevalence of depression among primary caregivers of patients with mental illness was 12 (19%). Out of those caregivers with depressions, 11.3, 3.5 and 4.2% had moderate, moderately severe and severe types of depression respectively. The prevalence of depression among female primary caregivers was 25% (n = 40). Being single (aOR 2.62, 95% CI = 1.07, 6.41), giving care more than six hours per day (aOR 3.75, 95% CI = 1.51, 9.33) and caring for a patient who had more than once episodes of suicidal attempts (aOR 1.48, 95% CI = 1.07, 3.42) were positively associated with depression among caregivers of patients with mental illness.ConclusionWe found that the prevalence of depression among primary caregivers was high. Depression among caregivers was associated with giving care more than six hours per day and caring for a patient who had two or more episodes of suicidal attempts. The prevalence of depression among female caregivers was higher than that of the male caregivers. Therefore, special focus should be given to primary caregivers spending long hours for providing care, those with low perceived social support; caregivers of patients with suicidal ideation and female caregivers.