The aim of this study was to describe the ovarian structure (OS) and its relationship with hyperandrogenism in girls with premature pubarche (PP). A pelvic ultrasound was carried out in 23 girls with PP and in 57 prepubertal age-matched controls (C), and the OS was subdivided into five classes (c): 1-homogeneous; 2-microcystic, 3-multicystic, 4-polycystic and 5-follicular. In the girls with PP, an ACTH test was performed, and the presence of hormonal levels >3 SD of postpubertal normal levels and not compatible with late-onset congenital adrenal hyperplasia were considered an exaggerated response. The fasting levels of glucose (G) and insulin (I) were measured and the fasting I to G ratio (FIGR) was calculated. FIGR >22 was suggestive of I resistance (IR). The microcystic structure (c2) was more frequently found in the PP than in the C group (63% vs 35%, p=0.03). In the PP group, we observed the following OS: cl (n=6), c2 (n=15), c3 (n=1) and c4 (n=1). 11-Deoxycortisol--both basal and after ACTH--was greater in the PPc2 group than in PPc1 (p=0.04, p=0.0008, respectively). We also observed an exaggerated response to ACTH in 87% of the girls with PP, greater in the PPc2 group than in PPc1 (p=0.04). The FIGR showed IR in 44% of girls with PP, but I levels and FIGR were similar between PPc1 and PPc2. These findings suggest generalized adrenocortical hyperresponsiveness in girls with PP, which is more accentuated in PPc2. Long-term follow-up of girls with PP into adulthood is warranted to ascertain whether microcystic ovarian structure precedes functional ovarian hyperandrogenism.