The study sought to evaluate the clinical, endocrinologic, and ultrasonographic features in 150 Singaporean adolescent girls with polycystic ovary syndrome (PCOS) before and after treatment, which was composed primarily of a combined hormone therapy of estrogen and cyproterone acetate. The patients' ages ranged from 12 to 22 years with the majority between 15 and 18 years of age. Most of these girls were seen between their third and fifth gynecologic year. A considerable proportion of them had matured early, experiencing menarche between 9 and 12 years of age. Tanner staging was normal except for a greater proportion at higher stages for pubic and axillary hair, most likely a reflection of the substantial degree of androgenization commonly found in subjects with PCOS. All 150 patients presented with menstrual disorders including secondary amenorrhea, menarche only, anovulatory uterine bleeding, oligomenorrhea, and primary amenorrhea. The majority had normal body weight; 10% to 27% were either underweight or overweight, respectively. On ultrasound, patients presented with enlarged ovaries; enlargement was more pronounced in the right ovary with dense stroma and multiple subcapsular cysts. Many subjects had elevated androgen, luteinizing hormone (LH), and LH/ follicle-stimulating hormone (FSH) levels. Although characteristic of PCOS, FSH levels were either low or normal. Prolactin, estradiol, dehydroepiandrosterone sulfate (DHEAS), and androstenedione were generally normal. A substantial proportion of the study group had elevated cortisol levels. It was noted that adolescent girls with PCOS responded well to treatment; more than 60% showed improvement in cycle profiles following at least 1 year of treatment. Our current opinion is that adolescents with PCOS should be managed early, and that treatment should include medical correction of any hormonal or body-weight imbalance and include psychologic intervention when necessary.