Of nearly 1900 live-born singletons, born from April 1988 to October 1989 inclusive, nine measurements of length and weight have been taken between the ages of 1 and 24 months. In the first part of the study, differences in attained length and weight at 1 and 2 years of age are analysed according to socioeconomic status (SES). Multiple regression analyses are used to investigate the association of SES and other background characteristics with length and weight. The second part focuses on the analysis of differences in linear length and weight gain in the first 2 years of life, using a two-step regression technique. At 1 and 2 years of age, differences in attained length and weight and in length and weight gain according to SES are small and not significant, except for the children of Mediterranean parents in the low-SES group, who are significantly heavier than children of all other groups and gain significantly more in weight compared to children of Dutch parents in the low-SES group. Of all the factors studied it appears that parental height, birthweight, parity and ethnic descent of the parents are associated with attained length and weight at 1 and 2 years of age. Of these factors, ethnic descent, however, is not associated with length gain. A small but statistically significant catch-up growth is found in children of mothers who smoked during pregnancy.