The safety of performing potentially difficult midcavity forceps or vacuum extractions, as trials of instrumental delivery was assessed retrospectively. Successful vaginal delivery was achieved in 61% of 122 patients with delay in the second stage who had a trial of instrumental delivery performed in an operating theatre with full preparations to proceed to caesarean section. The outcome was compared with that in 42 patients who were delivered for the same indication, by primary caesarean section, without prior instrumentation. Transient fetal trauma occurred only in the trials of instrumental delivery, and there was no significant difference in immediate neonatal or maternal morbidity. In another group of 61 patients instrumental delivery was attempted without full preparations for possible caesarean section and when unexpected difficulty arose, the forceps or vacuum extractor were abandoned in favour of caesarean section. Within this group of unexpected failures of instrumentation there were significantly more babies with low Apgar scores, delayed onset of respirations or needing intubation. A carefully conducted trial of instrumental delivery is an acceptable alternative to caesarean section for delay in the second stage due to a potentially difficult midcavity arrest.