Benign premature adrenarche (PA) is the term used to refer to girls with the early development of pubic hair before the age of 8 yr and is characterized by mild hyperandrogenism. Hyperandrogenism in adult women is often not as benign and has been associated with insulin resistance, acanthosis nigricans (AN), and the polycystic ovary syndrome. We have seen a group of young girls with PA who have also been found to have AN. The purpose of this study was to determine whether there are any clinical and biochemical differences in those girls with PA with and without AN. Twelve girls with PA were divided into two groups at the time of evaluation: group I, those without AN (n = 5); and group II, those with AN (n = 7). Adrenal androgen levels were determined in all subjects by a 60-min ACTH stimulation test. Insulin sensitivity was measured by the frequently sampled iv glucose tolerance test with tolbutamide and was assessed using the modified minimal model. Mean chronological age, bone age, and weight for length index were similar in the two groups. The baseline and stimulated levels of adrenal androgens were also not significantly different between the two groups. The group I girls (without AN) had an insulin sensitivity index of 6.75 +/- 1.31, which was in the normal prepubertal range. This was significantly different from that in group II (with AN), who had an insulin sensitivity index of 3.69 +/- 1.29. Therefore, many girls with premature adrenarche can have AN and decreased insulin sensitivity. Whether these girls have a truly benign course or are at risk of ovarian dysfunction or carbohydrate intolerance needs to be assessed.