The endocrine-metabolic hallmarks of polycystic ovary syndrome are hyperinsulinism, hyperandrogenism, dyslipidemia, and anovulation. We hypothesized that dyslipidemia and anovulation in nonobese women with polycystic ovary syndrome are essentially secondary to the concerted effects of hyperandrogenism and insulin resistance. We tested this hypothesis by comparing the efficacy of anti-androgen (flutamide) or insulin-sensitizing (metformin) monotherapy to that of combined therapy in normalizing the endocrine-metabolic and anovulatory status of nonobese, young women with hyperinsulinemic hyperandrogenism. Thirty-one young women (mean age, 18.7 yr; body mass index, 21.9 kg/m(2); hirsutism score, 16; monthly ovulation rate monitored by weekly serum progesterone, 10%) were randomly assigned to receive once daily flutamide (250 mg; n = 10), metformin (1275 mg; n = 8), or combined flutamide- metformin therapy (n = 13) for 9 months. At baseline, there were no endocrine-metabolic differences among treatment groups. Compared with monotherapy, combined flutamide-metformin therapy resulted in greater improvements in insulin sensitivity, in testosterone, androstenedione, dehydroepiandrosterone sulfate, and triglyceride levels, and in low-density lipoprotein/high-density lipoprotein-cholesterol ratio (all P < 0.005). Monthly ovulation rates increased after 9 months to 75 and 92%, respectively, with metformin alone or with combined therapy, but were unimproved with flutamide alone. All treatments were well tolerated. In conclusion, combined anti-androgen and insulin-sensitizing treatment in young, nonobese women with hyperinsulinemic hyperandrogenism had additive benefits on insulin sensitivity, hyperandrogenemia, and dyslipidemia. The data from this small study suggest that dyslipidemia is secondary to excess androgen action in concert with the hyperinsulinemia associated with insulin resistance. In contrast, anovulation seems to be mainly attributable to insulin resistance and hyperinsulinemia.