Today, many of the 10 million childhood deaths each year are caused by diseases of poverty--diarrhea and pneumonia, for example, which were previously major causes of childhood death in many European countries. Specific analyses of the historical decline of child mortality may shed light on the potential equity impact of interventions to reduce child mortality. In our study of the impact of improved water and sanitation in Stockholm from 1878 to 1925, we examined the decline in overall and diarrhea mortality among children, both in general and by socioeconomic group. We report a decline in overall mortality and of diarrhea mortality and a leveling out of socioeconomic differences in child mortality due to diarrheal diseases, but not of overall mortality. The contribution of general and targeted policies is discussed.