Pelvic ultrasound and hormonal studies were performed in 29 adolescent patients, aged 12 to 20 years, to evaluate menstrual irregularities. Patients were divided in three groups according to ultrasound ovarian volumes: group I (n = 16) both ovaries < 10 cm3; group II (n = 8) one of the ovaries > or = 10 cm3; and group III (n = 5) both ovaries > or = 10 cm3. Serum levels of LH, LH:FSH ratio, testosterone, and androstenedione were significantly higher (p < .05) in group III. Positive predictive value of both ovarian volumes > or = 10 cm3 in terms of polycystic ovary syndrome (PCOS) was 100%, negative predictive value was 81%, sensitivity was 63%, specificity was 100%. These data suggest that, in adolescent patients with menstrual disorders, bilateral ovarian volumes of higher than 10 cm3 are correlated with the diagnosis of PCOS.