We aimed to calculate the stillbirth rate at each gestation and also determine antenatal factors, which may be associated with unexplained stillbirth in a large UK teaching hospital. This was a retrospective study of all the stillbirths between January 1995 and October 1998. There were 27 170 births at S 24 weeks, gestation during the study period. Of these 161 were stillbirths giving a stillbirth rate of 5·9/1000; 149 (92·5%) were antepartum. Eighty-two (50·9%) were unexplained. The 'risk' of unexplained stillbirth per 1000 ongoing pregnancies was 0·3 at 24-25 weeks, fell steadily to 0·07 at 30-31 weeks and then rose to a peak of 1·16 at 40-41 weeks. About half (49·2%) of the pregnancies that ended in unexplained stillbirths had a normal antenatal course with no associated factors. Associated factors in the unexplained stillbirth group were identified in 50·8% of cases. The most common was intrauterine growth restriction, identified in 41·5% of cases. The 'risk' of stillbirth increases at term. No significant antenatal associated factor, detection of which would aid prevention, could be identified in the majority of cases.