This study examined the effects of the Bayley Scales of Infant Development (BSID) version on developmental outcomes among drug-exposed children, some of whom received an intervention. Developmental outcome was evaluated with the BSID at 12 and 18 months and with the BSID-II at 24 and 30 months. In the repeated measures analyses, children scored higher on the BSID Mental Developmental Index (MDI; p < .01) and Psychomotor Developmental Index (PDI; p < .01) than on the BSID-II MDI and PDI. Version x Time (p < .01) and Version x Group (p < .01) interactions were also found for the MDI but not the PDI. PDI scores decreased on both the BSID and the BSID-II (p < .01). Over the first 2 years postpartum, mean MDI and PDI scores decreased among these high-risk, drug-exposed children.