Sixty ventouse deliveries were analysed prospectively with specific attention paid to cup placement and its influence on successful or failed delivery. There was an 18.3% failure rate and 21.7% of all ventouse deliveries attempted had the cup inaccurately positioned. Cup placement was significantly more likely to be inaccurate when there was malposition of the fetal head. Significantly more tractions were needed when the cup was incorrectly positioned, but although there was a trend toward more failed attempts with the ventouse when the cup was inaccurately placed (23% vs 17%), this was not significant.