Cannabis, commonly called marijuana, is often used during pregnancy, likely due to the perception that it is a “safe” drug. Changes in legislation in many countries have lead to the increased availability of this drug and to its increasing use during pregnancy, often with other concomitant exposures such as alcohol, tobacco, and other drugs. Herein, we review the medical literature regarding effects of marijuana on the foetus and newborn. Possible effects of in utero exposure to marijuana focus on foetal growth, increase in the rates of stillbirth and preterm delivery, congenital malformations, and neurodevelopmental effects on the child. Published studies for all these outcomes are inconsistent. Foetal weight growth may be somewhat decreased, but the magnitude of this decrease is no greater than 100 g. There is insufficient evidence to conclude on any effect on the stillbirth rate. Although there are some reports of a slight increase in the rate of prematurity, most reports do not support this effect. Marijuana does not appear to be a major teratogen; however, a small increased risk for some congenital birth defects may be associated with early pregnancy use. Neurodevelopmental effects have been associated with marijuana use, but it is difficult to control for the effect of confounders. Despite the lack of conclusive evidence, it is important to remember that marijuana has not been shown to be a harmless drug during pregnancy and may affect the long-term neurodevelopment of the newborn infant.