Polycystic ovarian syndrome (PCOS) is a prevalent endocrinopathy in reproductive-age females, accredited to a chronic low-grade inflammatory reaction. Red distribution width (RDW), a parameter of complete blood count, was tested as an inflammatory marker ; higher RDW was linked to metabolic syndrome. We aimed to examine RDW in distinguishing PCOS-related metabolic and hormonal abnormalities. Methods : A case-control study recruited 128 women, divided into PCOS cases (64 / 128) and controls (64 / 128) according to Rotterdam criteria. Body mass index (BMI), estimated complete blood count parameters, hormonal markers (serum follicle-stimulating hormone (FSH), luteinizing hormone, and serum testosterone), and metabolic markers (HOMA-IR, serum high and low-density lipoprotein) were measured. Results showed that RDW was significantly higher in PCOS. HOMA-IR, LDL, testosterone, and LH / FSH were higher in PCOS and strongly correlated with RDW with positive correlations. HDL was elevated and correlated negatively with RDW in PCOS. ROC calculated (13.55) as RDW cut-off value for insulin-resistant with an AUC of 0.95, P < 0.001. In conclusion, a strong and remarkable correlation of RDW with metabolic abnormalities in PCOS cases with 100% sensitivity and specificity, in addition to being quick and inexpensive, makes it a reliable marker for screening for insulin resistance.