We have made endocrinologic, symptomatologic and utrasonographic studies in 38 adolescent (<18 years of age) patients with the complaint of hirsutism. 15 age-matched subjects were taken as control. The following results were obtained: 1-The causes of hirsutismus in the study group were polycystic ovarian syndrome (PCOS) (57.9%) (n=22), idiopathic hirsutism (IH) (39.5%) (n=15) and late-onset adrenal hyperplasia (LOHD) (2.6%) (n = 1). 2- Total testosterone (tT), free testosterone (fT), androstenedione (A) and dehidroepiandrostenedione (DHEAS) levels were significantly higher in hirsute patients than the controls. 3- There was no statistically significant difference in terms of luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin (PRL), thyroid stimulating hormone (TSH) and 17-hydroxy-progesterone (17-OHP) with the study group and the controls. 4-Menstrual irregularities were significantly higher in PCOS group than in the IH group. 5-In PCOS girls the mean ovarian volume and serum estradiol (E2) levels were significantly higher than IH group and controls. From the above findings, we suggest that clinical examination, endocrinologic and ultrasonographic investigation must be required in the evaluation of hirsute adolescent girls as considering the heterogenity of the etiology.