We examined 55 girls with isolated premature thelarche between the ages of 0.3 and 7.4 years (group A), 20 children with central precocious puberty between 2.1 and 7.7 years of age and 101 age-matched controls. The children with precocious puberty were divided according to distribution of pubic hair into group B (Tanner stages PH1, B2-3; n = 11), representing an early stage of the disorder, and group C (stages PH2-3, B3-4; n = 9), representing an advanced stage. Uterine and ovarian volumes were measured sonographically, peak serum levels of luteinizing hormone and follicle-stimulating hormone were determined after intravenous administration of luteinizing hormone-releasing hormone. The mean uterine and ovarian volumes were significantly greater in children with precocious puberty than in controls (group B: uterine volume: 3.8 +/- 2.0 ml vs 0.9 +/- 0.3 ml for controls, P < 0.001; ovarian volume: 2.2 +/- 1.3 ml vs 0.6 +/- 0.2 ml for controls, P < 0.01; group C: uterine volume: 8.0 +/- 4.4 ml vs 1.0 +/- 0.3 ml for controls, P < 0.01; ovarian volume; 2.6 +/- 1.3 ml vs 0.4 +/- 0.1 ml, P < 0.01). No significant differences were found between children with premature thelarche and the control group. As a diagnostic method for the early detection of central precocious puberty, ultrasound measurement of uterine volume had a sensitivity and specificity of 100% (cut-off value, 1.8 ml), while ultrasound determination of ovarian volume had a sensitivity of 82% and a specificity of 95% (cut-off value, 1.2 ml).(ABSTRACT TRUNCATED AT 250 WORDS)