This study investigated family patterns of morbidity in early childhood related to different degrees of severity of morbidity, sex, birth-order position, and social class. The study was performed using data collected by the Continuous Morbidity Registration Project of the Department of Family Practice of the Nÿmegen University in the Netherlands. All recorded morbidity and a number of sociodemographic data (sex, birth order, and social class) were available. The study population included children (783 boys, 730 girls) born in the four practices from 1971 to 1985 and their parents. The children were followed until age five. Morbidity of children during the first five years of life and their parents during the same five years was categorized into three levels of seriousness and 10 morbidity groups. Correlations between morbidity of children and their mothers were high, particularly for nonserious morbidity (0.45-0.49). Correlations between morbidity of fathers and their children were similar for moderate and nonserious morbidity (0.30). Logistic regression analysis showed that the morbidity of the mother was the most important factor in predicting childhood morbidity. Although morbidity in early childhood was associated with sex, birth order, and social class, the morbidity of the parents, in particular the mother, was by far the most important factor.