To determine the incidence and outcome of unbooked pregnancies in women at the Rotunda Hospital Retrospective case control study. All unbooked deliveries in the Rotunda Hospital over a two year period were identified and matched with a control. Control patients were selected as the next delivery after each case and were regular antenatal attenders. Demographic and obstetric data was collected from each case and control and compared using the Chi-square test. There were 101 unbooked women in the study, during this time there were 11522 deliveries giving an incidence of unbooked pregnancies of 0.88%. Unbooked women were found to be young, multiparous, unemployed and unmarried. They were more likely to deliver by spontaneous vaginal delivery to preterm, low birth weight infants and were at greater risk of a stillbirth and neonatal death. Unbooked pregnancies account for a small proportion of our antenatal population. However, perinatal outcome is significantly worse in unbooked patients compared to those who are regular antenatal attenders.