The obstetrical, neonatal, and childhood risk associated with prenatal smoking are well known. Prenatal smoking has been implicated in up to 25% of low birth weight infants primarily from preterm birth and fetal growth restriction and up to 10% of all infant mortality. The relationship between prenatal marijuana smoking and obstetrical and infant outcomes is less clear. Marijuana is the most commonly used illicit drug during pregnancy. Neither exposure to cigarette nor marijuana smoke has evidence for teratogenicity, but both have been implicated in developmental and hyperactivity disorders in children. Pregnant women should be counseled on the risk of both cigarette and marijuana smoking.