Background: Premature ovarian insufficiency (POI) is the preferred term for the condition that was previously referred to as premature menopause or premature ovarian failure. The condition differs from menopause in that there are varying and residual ovarian functions. This study aimed to analyze the clinical characteristics of infertile women with premature ovarian insufficiency. Material & Methods: This prospective study was conducted at the OPD of Impulse Fertility Center, Impulse Hospital, Dhaka, Bangladesh. The study was conducted for a period from January 2022 to December 2022. A total of 23 patients who received outdoor treatment during the study period were purposively selected as sample size. A purposive sampling technique was followed in this study. After approval by the Ethics committee of the Hospital, informed consent from the respondents was obtained after explaining the purpose of the study to them. To be included in the study, respondents should have met the classical definition of infertility defined by the WHO as the inability of a sexually active non-contraceptive using woman to have a live birth after 12 or more months of regular sexual intercourse without a malefactor. Women who had male-factor infertility were excluded. In this study live birth was used as a measure of proven fertility (Because couples desire children, not simply pregnancies, infertility affects couples regardless of whether the etiology lies in conception or the progression of the pregnancy). All the necessary laboratory investigations were done. A questionnaire was developed and data were collected by interviewing the patients and some data were collected from the laboratory results. Data were processed and analyzed by SPSS 19 version. Results: All patients had normal puberty, and menarche occurred at ages 11–15, followed by a regular menstrual cycle. Women who presented with oligomenorrhea were younger than patients with infertility. The mean period of oligomenorrhea before diagnosis was 0.9 years in the oligomenorrhea group and 1.8 years in the infertility group. The mean age when the infrequent periods started was 28 years in the group with oligomenorrhea and 29 years in the group with infertility, and their anthropometric characteristics were not different. In most patients, the FSH levels on day 3 of their menstrual cycle were less than 25 mU/ml. FSH levels >25 mU/ml were confirmed in two patients with oligomenorrhea and five patients in the infertility group. AMH levels were low than 1.0 ng/ml (considered to be in poor ovarian reserve ranges: from 0.13 to 1.0 ng/ml in patients with oligomenorrhea and from 0.13 to 0.9 ng/ml in the infertility group. Transvaginal ultrasound-determined AFC on menstrual cycle days 4–8 was accessed in all patients. We consider AFC < 6 small follicles (diameters 3–9 mm) as a low ovarian reserve indicator. The lowest AFC (one small follicle) was noted in one infertile patient with oligomenorrhea. Conclusion: This study concluded that the subjects usually present with menstrual irregularity (oligomenorrhea) or infertility, and after proper evaluation, their poor ovarian reserve can be confirmed and an occult form of POI established. women who presented with only oligomenorrhea were younger than infertile patients; therefore, menstrual irregularity may be the earliest clinical symptom of occult POI.