Growth and neurodevelopment at 6, 10 and 18 months of age have been studied prospectively and longitudinally in a series of 17 children born to mothers who used benzodiazepines (BZD) in therapeutic doses as their only psychotropic drug throughout pregnancy. The results were compared with a group of 29 children born to mothers without any known use of psychotropic drugs. The BZD-exposed children caught up their low mean birth-weight, at an early stage, whereas the slightly decreased head circumference at birth remained at the same low level. In five infants, a pattern of craniofacial anomalies was found. Deviating neurodevelopmental and clinical symptoms and signs were common. The gross motor development was retarded at 6 and 10 months, but was nearly normal at 18 months. Impaired fine motor functions were found on all follow-up occasions. At 18 months, the most prominent finding was a delayed development of pincer grasp. The BZD-exposed children showed deviations in muscle tone and pattern of movements more frequently than children in the reference group. The study suggests that the use of BZD in therapeutic doses throughout pregnancy can have negative effects on the development of children up to 18 months of age. The long-term hazards cannot be evaluated from these results. A further follow-up at early school age is needed and is in progress.