Objective To determine uterine and ovarian size in Turner syndrome (TS) and to compare uterine and ovarian size evaluated by transabdominal ultrasound (US) and magnetic resonance imaging (MRI) in girls with TS and two groups of controls. Design A cross-sectional study. Patients Forty-one girls with TS (17·0 ± 3·3 years, range 11·2-24·9 years), 50 healthy age-matched controls (16·9 ± 3·2 years, range 12·5-25·0 years) and 107 Tanner-stage-matched controls (15·0 ± 3·2 years, range 10·1-24·2). Measurements Uterine and ovarian volume by US and MRI. Results Ovaries were detected in 37% in TS by US and in 55% in TS by MRI (P = 0·1). Total ovarian volume was lower in TS compared to both groups of controls (TS vs C-US: median 1·1 ml (range 0·1-29·3) vs 11·52 ml (1·9-77·9), P = 0·001, TS vs C-MRI: 1·0 ml (0·1-34·2) vs 13·2 ml (2·4-30·1), P