OBJECTIVE: Insulin resistance (IR) is frequent in polycystic ovary syndrome (PCOS) and contributes to the increased risk for type 2 diabetes mellitus and cardiovascular disease of this population. Several markers of IR are used but most are expensive or have limited sensitivity and specificity. Preliminary data suggest that the menstrual cycle pattern correlates with IR in PCOS but existing studies are small. We aimed to assess the relationship between the type of menstrual cycle irregularities and IR in PCOS.DESIGN: Prospective study.METHODS: We studied 1285 women with PCOS, divided according to the menstrual cycle pattern.RESULTS: Patients with isolated secondary amenorrhea and those with secondary amenorrhea alternating with regular menstrual cycles were more insulin resistant than patients with regular cycles (Group D). Patients with isolated oligomenorrhea were also more insulin resistant than Group D. However, patients with oligomenorrhea alternating with regular cycles, secondary amenorrhea, or polymenorrhea had comparable levels of markers of IR with Group D. Moreover, patients with oligomenorrhea alternating with regular cycles were less insulin resistant than patients with secondary amenorrhea alternating with regular cycles. Finally, patients with isolated polymenorrhea and those with polymenorrhea alternating with regular cycles had comparable levels of markers of IR with Group D.CONCLUSIONS: Amenorrhea is associated with more pronounced IR in PCOS, and oligomenorrhea portends a less excessive risk for IR than amenorrhea whereas polymenorrhea appears to be even more benign metabolically. Therefore, the type of menstrual cycle abnormality appears to represent a useful tool for identifying a more adverse metabolic profile in PCOS.