The low contraceptive prevalence rate and the existence of unmet demand for family planning services present a challenge for parties involved in family planning research in Tanzania. The observed situation has been explained by the demand-side variables such as socioeconomic characteristics and cultural values that maintain the demand for large families. A small, but growing body of research is examining the effect of supply-side factors such as quality of care of family planning services on the demand for contraceptives. This paper analyses the demand and supply factors determining contraceptive use in Tanzania using the Tanzania Service Availability Survey (1996) and the Tanzania Demographic and Health Survey (1996) data sets. The results show that access to family planning services and quality of care of services are important determinants of contraceptive use in Tanzania even after controlling for demand-side factors.