The effect of rate of growth and relative weight in childhood on adult mortality was studied among 13,146 persons whose weights and heights were measured between the ages of 5 and 18 years in Hagerstown, Maryland, during the period 1933-1945. Relative weight was defined internally, age- and sex-specific Z-scores for height and weight were calculated using national standards, and height and weight velocities were measured as annual increments. Associations between growth parameters (pre- and postpubertal) and mortality through 1985 were investigated in subjects who matched the 1963 and 1975 private health censuses of Washington County, Maryland, using a nested case-control design. Odds ratios of mortality increased linearly with prepubertal relative weight (p less than 0.05 for both sexes combined) and with postpubertal relative weight in females (p less than 0.01). The associations between growth velocities or attained height with mortality tended to be inverse, although not statistically significant. These results are compatible with the existence of positive associations of overweight in school-age children with long-term mortality and seem to allay fears that harm could come from increased growth rates in childhood. Without jeopardizing growth, the avoidance of overweight in childhood might reduce mortality in middle age.