The net effects of various factors on length at birth and height at 5 years were determined in 3,707 single-born white California children. First-born children were significantly short at birth, but taller than average at 5 years. Children born to women with early menarche and children of older parents were average in birth length but taller than average at 5 years. Length and weight at birth showed significant correlations with height at 5 years. The child small at birth was most likely to catch up with his peers at age 5 if short gestation caused small birth size. Children of smoking mothers were short at birth and at 5 years. Socioeconomic factors (income, education, and occupation) appeared to be of little importance as determinants of growth. Of the total variation in height at age 5 years which is explained by the factors considered, parental height alone accounted for 88.6%; all other factors for 11.4%.