The psychoactive recreational drug 3,4-methylenedioxymethamphetamine (MDMA) is widely abused. The fact that MDMA induces neurotoxic damage in serotonergic nerve endings is well known. However, the effects of MDMA on pregnant and neonatal animals remain unknown. Therefore, we studied the effects of gestational exposure to MDMA on birth, growth, and behavior of pups. Female BALB/c mice were orally administered either water (10 ml/kg) or MDMA (20 mg/10 ml/kg) from gestational day 1 to postnatal day (P) 21. MDMA did not affect the birth rate, but the survival rate of the pups significantly decreased. A significant reduction in body weight gain was observed in pups from MDMA-administered dams during P3-P21. Maternal MDMA treatment caused an attenuated cliff avoidance reaction and decreased motor function in the pups, as determined by the wire hanging test. These results suggest that MDMA treatment during pregnancy and lactation causes growth retardation and dysfunction of motor neurons in mouse pups.