The aim of the present study was to determine whether a group of patients selected on the basis of clinical features only is characterized by the typical hormonal findings as discussed in the literature concerning the PCO-syndrome. PCO patients had oligomenorrhea, secondary amenorrhea or otherwise evidence of chronic anovulation, as well as hirsutism and/or obesity. Control women had regular menstrual cycles and a normal body weight. Since androgen and estrogen production in women depends on the stage of follicular development, an effort was made to obtain endocrinological data under standardized conditions. Under well-defined circumstances the PCO group (n = 20) had higher LH levels and lower FSH levels as compared with the control group (n = 10). Consequently the LH/FSH ratio was significantly elevated in the PCO group. Serum estrone and estradiol levels were significantly elevated in the PCO group, as were the serum levels of androstenedione and testosterone. Despite these differences a marked degree of overlap existed in the PCO patients and the control women for gonadotropin, estrogen and androgen levels. It was concluded that although the presence of polycystic ovaries in the investigated PCO group of women was not confirmed by laparoscopy, laparotomy or histological examination of the ovaries, these women had basal endocrinological characteristics similar to those found in well-proven PCO patients reported in the literature.