Our purpose was to compare perinatal mortality between twins and singletons matched for gestational age at delivery with the hypothesis that perinatal mortality would be similar. A retrospective cohort study compared perinatal mortality in twins (790 babies) matched for gestational age at delivery at > or = 30 weeks with the next singleton. Perinatal mortality was also compared by expected growth (small and average for gestational age) and by the cause of the preterm delivery (medical indication, spontaneous preterm delivery, or preterm premature rupture of membranes with preterm delivery. Uncorrected perinatal mortality was significantly greater in singletons (56/1000) than in twins (26/1000) (p = 0.004). After major congenital anomalies were excluded, perinatal mortality remained significantly higher in singletons (25/1000) than in twins (11/1000) (p = 0.04). In preterm deliveries perinatal mortality was significantly greater in singletons (72/1000) than in twins (19/1000) (p = 0.0002). Perinatal mortality was significantly greater in small- compared with average-for-gestational-age neonates, whether singletons or twins (p = 0.005), and singleton small-for-gestational-age neonates had a significantly greater perinatal mortality (105/1000) than did twin small-for-gestational-age neonates (36/1000) (p = 0.02). Perinatal mortality was not significantly different between preterm singletons and twins delivered by spontaneous preterm labor. However, perinatal mortality in preterm singletons delivered for a medical indication (156/1000) was significantly greater than for twins (20/1000) (p = 0.0006). At > or = 30 weeks at delivery, twins either had a perinatal mortality similar to, or less than singletons matched for gestational age at delivery. This suggests that when preterm delivery is controlled for perinatal mortality is not greater in twins. In twins, without risk factors for perinatal death, routine antepartum testing may not be indicated.