Objective: To determine the relationship of different clinical, biochemical parameters and hormonal assay with the BMI of women who are known to have PCOS, and to compare these demographic features with intrafamily marriages. Materials and Methods: From January 2005 until December 2006, patients attending the infertility clinic at Aga Khan University Hospital, Karachi, were evaluated for their clinical features. Couples were divided into 2 groups: group A had a history of first-degree intrafamily marriages, and group B had none. Complete biochemical evaluation was performed by day-2 serum FSH, LH, prolactin, testosterone and fasting serum insulin levels.The results were recorded on a data collection form. Ultrasonic evaluation was performed with transvaginal ultrasound to check the morphological appearance of the ovaries. A modified glucose tolerance test with 75 g glucose was performed and the results were recorded as normal, impaired and abnormal. Insulin resistance was calculated using the HOMA index method. Results: During this period 203 patients were evaluated for demographic and biochemical features of PCOS. The prevalence of obesity was 70% with 59.3% women found to have hyperinsulinemia while 52.3% of patients had insulin resistance according to the HOMA index method. Univariate and multivariate analyses were used to compare the 2 groups. A linear relationship between oligomenorrhea, family history of diabetes, tonic LH, high fasting serum insulin levels, insulin resistance and an abnormal glucose tolerance test was revealed, keeping intrafamily marriage and BMI as dependent variables. In this population 48% of couples were in first-degree intrafamily marriages, suggesting the possibility of a high genetic predisposition for abnormal metabolic features beside ethnic predisposition. Conclusion: A linear relationship of high BMI and family marriages has been seen with insulin resistance, oligomenorrhea and impaired glycemic control. The number of obese women and the high rate of intrafamily marriages make our population genetically susceptible to metabolic complications.