In a response to the dearth of valid development assessment instruments in Nigeria, this study sets out to validate the Developmental Screening Inventory (DSI) against a performance developmental instrument, i.e. the Bayley Scales of Infant Development (BSID). Each member of a group of 128 healthy Nigerian children, obtained by selecting 16 of them from each of eight developmentally distinct age sub-groups (8,16 and 32 weeks and 10, 12,18,24 and 30 months), were tested on both instruments under controlled conditions. Reliability based on Cronbach's correlation coefficient was found to be significantly high (p < 0.01) at a value of +0.64, and scores of both instruments correlated significantly indicating satisfactory validity. Cheapness and ease of administration, as reported elsewhere, further enhance the suitability of DSI as an instrument for use in paediatric practice in Nigeria and probably in other African countries.