We determined the hormonal, metabolic and ultrasonographic pattern of adolescents with menstrual irregularity since menarche but without clinical signs of hyperandrogenism with the aim of evaluating whether this condition represents an early stage of polycystic ovary syndrome (PCOS). These adolescents were divided in two groups: 13 adolescents with irregular cycles (IC) within the first 3 postmenarchal years (IC < or = 3) and 15 adolescents having persistent irregular cycles for more than three postmenarchal years (IC > 3). These adolescents were compared with 15 adolescents with PCOS and 18 normal adolescents. The values of free testosterone, free androgen index, luteinizing hormone (LH) and LH/follicle-stimulating hormone (FSH) ratio were similar in IC < or = 3, IC > 3 and PCOS, and higher than in the normal group (p < 0.005). The total testosterone and androstenedione levels were higher and sex hormone-binding globulin (SHBG) lower in PCOS only when compared with the normal group (p < 0.05). The ovarian volume was similar in IC < or = 3, IC > 3 and PCOS, and higher than in the normal group (p < 0.005). A higher incidence of polycystic structure was found in IC < or = 3, IC > 3 and PCOS, whereas normal structure was more common in normal adolescents (p < 0.0005). There were no significant differences in glucose and insulin parameters between groups. These results indicate that menstrual irregularity within the first postmenarchal years can be an early clinical sign of PCOS.