PCOS (polycystic ovarian syndrome) one of the most common hormonal endocrine pathology in female of reproductive age. Prevalence ranges between 5% to 15% based on the criteria of diagnosis. The pathophysiology of PCOS is a complex interaction of between genetics, epigenetics, ovarian dysfunction, endocrine, neuroendocrine and metabolic alterations, amongst other changes. Elevated LH concentrations can be observed in approximately 40-60% of women with PCOS. This is a major sign of neuroendocrine dysfunction because of an increase in the amplitude and frequency of LH pulses, which most likely reflect an increase in GnRH pulse frequency. PCOS have an adverse effect on cardiovascular system. PCOS has two phenotypes lean PCOS and obese PCOS. Small but significant proportion of patients are present with normal body mass index (BMI; ≤25 kg/M2), they are termed as lean PCOS. They may or may not have irregular menstrual cycles and other issue like acne and alopecia. Some clinical signs are same in both the lean and obese phenotypes which make the therapeutic approach difficult. Methodology: This is a study of prevalence of PCOS based on BMI classification. The inclusion criteria were women diagnosed with PCOS within the age group of 18 to 30 years.120 samples were collected and analysed. Results: Out of total population, 58.3% women with normal BMI which was highest. about 18.3% women comes under pre-obesity class. On further classification 18.3% women with BMI less than 18 come under the underweight category which is lean category.3.3% women with BMI range of 30-34.9 have been detected with PCOS. Conclusion: From the conducted study it was concluded that, though minor but there is significant presence of PCOS in lean women. Lean women are also at a risk of developing PCOS. obesity cannot be considered as a confirmatory factor for diagnosis of PCOS