From 1998 the population-based North of England Multiple Pregnancy Register (MPR) has collected data on all multiple pregnancies in the region from the earliest point of ascertainment in the pregnancy. This article describes the development of the MPR and the findings of the first 5 years of data collection. Mothers now give explicit consent for their inclusion with named data, in accordance with section 60 of the Health and Social Care Act 2001. During 1998 to 2002, 2310 twin pregnancies were registered, with an increasing twinning rate of 13.6 to 16.6 per 1000 maternities. Chorionicity ascertainment in twin maternities with at least one stillbirth or live birth has improved from 81% in 1998 to 91% in 2002. Before 24 weeks of gestation, 8.4% (359/4620) of fetuses were lost either spontaneously or as a result of termination of pregnancy. The perinatal mortality rate was much higher in monochorionic than dichorionic twins, mainly due to differences in stillbirth rates (49.0 vs. 11.5 per 1000 maternities respectively, risk rate = 4.2; 95% confidence intervals 2.7-6.6). The gestational-age-specific neonatal mortality rates were similar in twins and singletons, except in the group of term births (> or weeks' gestation) when compared by conventional gestational age categories. For stillbirths, the rates were even lower than in singletons in gestational age categories of less than 32 weeks. The register is an important resource of data on multiple pregnancies, which allows monitoring of trends in multiple birth rates and pregnancy losses and provides a unique opportunity for etiological and long-term follow-up studies.