In Amsterdam a longitudinal, prospective and multidisciplinary study on the development of infants of drug-dependent mothers (IDDM) was started in 1983: 35 IDDM and 35 reference infants were originally enrolled. The drug-dependent women had used combinations of methadone, heroin, cocaine and other drugs during pregnancy. Of the IDDM, 80% had to be treated pharmaceutically for neonatal abstinence symptoms (NAS). Physical, neurological, cognitive and the socio-emotional development of the children were studied regularly from birth until 5.5 years of age. Differences between the reference group and the IDDM were found most clearly in cognitive development. The IDDM also had more behavioural problems at some of the ages studied. No group differences were seen in motor development. So far the results of the study show that IDDM and their caregivers need extra support in order to improve early communication and the children's cognitive development.