Exaggerated adrenal response (ExAR), i.e. hypersecretion of both 17-hydroxypregnenolone (170HPreg) and 17-hydroxyprogesterone (170HP) in response to adrenocorticotropic hormone (ACTH) stimulation, is frequently found in women with polycystic ovary (PCO) syndrome who had precocious adrenarche. In an earlier study we found an abnormal adrenal response in girls with idiopathic true central precocious puberty (CPP) at early stages of puberty. On follow-up it was noted that a significant number of girls with CPP develop PCO-like syndrome at a relatively young age. The aim of the present study was to determine if there is an association between ExAR and early PCO in girls with a history of CPP. Included were 49 girls with a history of CPP, 34 of whom were treated with gonadotropin-releasing hormone (GnRK) analog. All 49 were evaluated at full maturity, at ages 12.5-14 years, 0.5-4 years after menarche or resumption of menses. Of the 49 girls, 20 had at least 3/4 clinical signs of PCO (irregular menses, hirsutism, acne and obesity) and were defined as PCO-like+, whereas 29 did not fulfil the criteria and were considered PCO-like-. Girls with a definite enzyme deficiency were excluded from the study. All participants underwent a combined iv ACTH-GnRH test at early follicular phase. The PCO-like+ girls all revealed ExAR, i.e. an elevated stimulated 170HPreg of 63.4 ± 9.6 nmol/l (normal 28.6 ± 9.2 nmol/l) and a normal stimulated 170HPreg/ 170HP ratio of 7.1 ± 1.8 (normal 6.2 ± 2.7), whereas all the PCO-like- had a normal adrenal response (30.0 ± 8.7 and 5.3 ± 2.0 nmol/l, respectively). Compared to the PCO-like- girls, those with PCO-like ± had significantly higher levels of testosterone (1.8 ± 0.7 vs 1.0 ± 0.5 nmol/l; p < 0.001), androstenedione (6.6 ± 3.2 vs 4.7 ± 1.8 nmol/l; p < 0.02) and dehydroepiandrosterone sulfate (7.8 ± 4.7 vs 4.2 ± 2.5 μmol/l; p < 0.004), and a trend toward inappropriate luteinizing hormone secretion. The prevalence of ExAR (40.8%) in the mature CPP girls (confined to only PCO-like+) was similar to that previously found by us in another group of girls with CPP at early puberty (44.6%). In conclusion our findings indicate that the pattern of adrenal response remains unchanged from early puberty to adulthood and is probably inherent. As only the girls with CPP who developed early PCO syndrome showed ExAR, it is suggested that ExAR in early puberty may serve as a predictive marker for the eventual development of PCO.