To evaluate pregnancy outcome of assisted reproductive technology (ART)-conceived twin pregnancies.Retrospective study.A tertiary obstetric care center.All twin pregnancies deliveredor = 24 weeks of gestation from January 1, 1996, to December 31, 1997.Maternal and neonatal record review.Pregnancy and perinatal outcome.The study group comprised 104 ART-conceived twin pregnancies, and 193 non-ART-conceived pregnancies served as controls. Mean maternal age, the proportion of nulliparae, and the percentage of women who delivered before 34 weeks' gestation was higher among the study women, whereas mean gestational age was younger. The incidences of pregnancy-induced hypertension, uterine bleeding, premature contractions, intrauterine growth retardation, fetal death, discordance, and cesarean section were significantly higher in the study group. Correspondingly, in the study group, the mean birth weight of both twins was lower; more neonates weighed1, 500 g, more had Apgar scores of7 at 5 minutes, more were admitted to the intensive care unit, and more second twin neonates died. The outcome of twin pregnancies conceived spontaneously was comparable with those conceived by ovulation induction.Assisted reproductive technology-conceived twin pregnancies are at greater risk than non-ART-conceived ones for pregnancy complications and adverse perinatal outcome.