Background. The polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders affecting reproductive-age women. Increased insulin resistance, a major risk factor for the development of type 2 diabetes mellitus, is an important feature of PCOS, occurring in 50-70 percent of cases. However, because of significant racial variations in the clinical presentation of PCOS, the prevalence of insulin resistance in PCOS differ among different populations. The Philippines presently has no data on the prevalence of insulin resistance among PCOS women Homeostasis model assessment (HOMA), a simple method used to derive an estimate of insulin resistance from the mathematical modeling of fasting plasma glucose and insulin concentrations, has been validated against independent measures of insulin sensitivity and beta-cell function Objectives. To assess the prevalence of insulin resistance and to determinse the parameters associated with increased risk for insulin resistance among Filipino PCOS women Methodology. Patients 16-40 years old from private Endocrine, Reproductive and Fertility Clinics of St. Lukes Medical Center (SLMC) between January to October 2003 diagnosed with PCOS by two minimal criteria - menstrual dysfunction and hyperandrogenism were enrolled in the study. Insulin resistance by HOMA score was calculated using the formula: HOMAIR = fasting serum insulin (uU/ml) X fasting plasma glucose (mmol/L)/22.5. Beta-cell function and insulin sensitivity were determined from the MSDOS-based HOMA computer program of Levy et al Results. Thirty seven PCOS women were included in the study. Nineteen were seen at the Endocrine clinics while 18 were from the Reproductive clinics. The mean age was 28.7 +/- 6.4 years. Fasting glucose was normal in 91.9 percent. Two women were classified as diabetic by ADA criteria, while 1 had impaired glucose tolerance. Mean HOMA-IR for PCOS women was 4.1 +/- 3.3 Conclusion. The prevalence of insulin resistance, defined by a HOMA-IR value of 1.4, is 93.3 percent in women with PCOS at SLMC. Fasting serum insulin is the only consistent parameter significantly associated with insulin resistance in this population of women.