Anterior fontanelle (AF) dimensions were studied in 337 normal and apparently healthy Nigerian infants aged from 1 week to 12 months in Ibadan, Nigeria. Mean anterior fontanelle size fell from 3.4 cm in neonates to 2.5 cm at 4-6 months and to 0.8 cm at 10-12 months. The anterior fontanelle was closed in 11% of 4-6-month-olds and 53% of 10-12-month-olds. The mean AF size in neonates was larger than published figures from Caucasian and Chinese populations, but at 12 months mean AF size in Nigerian infants was smaller than published Caucasian and Chinese figures. The quartiles of the distribution of the AF size are also presented. It is concluded that there may be important racial differences in AF sizes and closure and closure frequencies in the 1st year of life and that appropriate local references should be used when attempting to classify a given AF size as normal or abnormal.