There is debate about the role of the private sector in providing services in the health systems of low- and middle-income countries and about how the private sector could help achieve the goal of universal health coverage. Yet the role that the private sector plays in the delivery of health services is poorly understood. Using data for the period 1990-2013 from 205 Demographic and Health Surveys in seventy low- and middle-income countries, I analyzed the use of the private sector for the treatment of diarrhea and of fever or cough in children, for antenatal care, for institutional deliveries, and as a source of modern contraception for women. I found that private providers were the dominant source of treatment for childhood illnesses but not for the other services. I also found no evidence of increased use of the private sector over time. There is tremendous variation in use of the private sector across countries and health services. Urban and wealthier women disproportionately use the private sector, compared to rural and poorer women. The private sector plays an important role in providing coverage, but strategies to further engage the sector, if they are to be effective, will need to take into consideration the variation in its use.