ABSTRACT Objectives To investigate the effect of endometrial scratching, performed during oral contraceptive pill (OCP) pretreatment, on reproductive outcome and on ultrasound markers of endometrial receptivity, and to assess the pain involved in the procedure, in unselected women undergoing assisted reproductive techniques (ART). Methods Women undergoing ART were randomly allocated to undergo either endometrial scratching with a pipelle de Cornier or a sham procedure, 7–14 days before starting controlled ovarian stimulation (COS). We evaluated subsequent rates of clinical pregnancy, live birth, implantation, miscarriage and multiple pregnancy. Pain during the procedure was evaluated using a 10‐cm visual analog scale. Endometrial thickness and volume and three‐dimensional power Doppler (3D‐PD) indices (vascularization index (VI), flow index (FI) and vascularization flow index (VFI)) were assessed during COS when there was at least one follicle ≥ 17 mm in diameter. Results We included 158 women. Endometrial scratching was associated with higher rates of live birth (41.8% vs 22.8%, P = 0.01) and clinical pregnancy (49.4% vs 29.1%, P = 0.01) and higher pain score (6.42 ± 2.35 cm vs 1.82 ± 1.52 cm, P < 0.001), endometrial VI (3.71 ± 1.77 vs 2.95 ± 1.56, P < 0.01) and VFI (0.97 ± 0.51 vs 0.76 ± 0.40, P < 0.01). There was no significant effect of endometrial scratching on rate of miscarriage (15.4% vs 21.7%, P = 0.53) or multiple pregnancy (22.5% vs 25.0%, P = 0.79), or on endometrial thickness (10.12 ± 1.55 mm vs 9.98 ± 1.62 mm, P = 0.59), endometrial volume (6.18 ± 1.63 cm3 vs 6.01 ± 1.48 cm3, P = 0.51) or FI (26.12 ± 2.82 vs 25.91 ± 2.72, P = 0.65). Conclusions Endometrial scratching performed once, during OCP pretreatment 7–14 days before starting COS, increases the chance of live birth and clinical pregnancy, but might cause considerable pain. Copyright © 2013 ISUOG. Published by John Wiley & Sons Ltd.