The purpose of this study was to evaluate mental and psychomotor development in infants of mothers whose asthma was actively managed during pregnancy and to compare the results with those froms infants of non-asthmatic mothers. Bayley Scales were assessed at age 15 +/- 3 months in 379 infants of asthmatic mothers and 376 control infants. Relationships were assessed between developmental indices and asthma severity, socioeconomic status, and infant prematurity. No significant differences in developmental indices were observed between infants of asthmatic mothers and control infants. No relationships were identified between developmental indices and maternal asthma severity. In the infants of both asthmatic and control mothers, a lower mean psychomotor developmental index was associated with birth weight < 2,500 g, and a lower mental developmental index with lower socioeconomic status. Hence, infants of asthmatic mothers whose asthma has been actively managed during pregnancy have developmental outcomes at 15 months of age that are similar to those of control infants.