There is an increased prevalence of maternal substance abuse during pregnancy in younger women in all socioeconomic classes and races. Our aim was to determine the prevalence and correlates of self-reported substance abuse among pregnant women and obstetric complications or neonatal outcomes in Iran. This retrospective cohort study is covering a five year period on medical records of pregnant women attending the maternity unit of four major hospitals (Mahdieh, Taleghani, Imam Hossein and Akbarabadi Hospitals). Women who reported using opium, heroin, crack, cannabis or methamphetamine were compared with women with no reported history of drug abuse for obstetric complications and prenatal morbidity and neonatal mortality. From 100,620 deliveries substance abuse was recorded for 519 women giving a prevalence of 0.5%. Opium was the most prevalent substance abused followed by crack (a mix of heroin and amphetamines). The exposed group had significantly more obstetric complications including preterm low birth weight and postpartum hemorrhage than the non-exposed group. The exposed group had significantly worse prenatal outcomes including more admissions to intensive care unit and higher infant mortality than the non-exposed group. None of the women in the exposed group was on methadone treatment at time of delivery. Risks of maternal and neonatal complications were increased in substance using pregnant women, especially preterm birth and low birth weight. We recommend a multidisciplinary team to provide methadone maintenance therapy for substance using pregnant women and urinary screen of all pregnant women presenting to hospital.