Previous studies have lacked sufficient power to assess associations between early-life socioeconomic position and adult cause-specific mortality. The authors examined associations of parental social class at age 0-16 years with mortality among 1,824,064 Swedes born in 1944-1960. Females and males from manual compared with nonmanual childhood social classes were more likely to die from smoking-related cancers, stomach cancer, respiratory disease, cardiovascular disease, and diabetes. Males from manual compared with nonmanual social classes were more likely to die from unintentional injury, homicide, and alcoholic cirrhosis. The association with stomach cancer was little affected by adjustment for parental later-life and own adult social class or education. For other outcomes, educational attainment resulted in greater attenuation of associations than did adjustment for adult social class. Early-life social class was not related to suicide or to melanoma, colon, breast, brain, or lymphatic cancers or to leukemia. With the exception of stomach cancer, caused by Helicobacter pylori infection acquired in childhood, poorer social class in early life was associated with diseases largely caused by behavioral risk factors such as smoking, physical inactivity, and an unhealthy diet. Educational attainment may be important in reducing the health inequalities associated with early-life disadvantage.