BACKGROUND: Improving access to facility-based delivery care has the potential to reduce maternal and newborn deaths across settings. Yet, the access to a health facility for childbirth remains low especially in low-income settings. To inform evidence-based interventions, more evidence is needed especially accounting for demand- and supply-side factors influencing access to facility-based delivery care. We aimed to fill this knowledge gap using data from Tanzania. METHODS: We used data from a cross-sectional survey (conducted in January 2012) of 150 health facilities, 1494 patients and 2846 households with women who had given births in the last 12 months before the survey across 11 districts in three regions in Tanzania. The main outcome was the place of delivery (giving birth in a health facility or otherwise), while explanatory variables were measured at the individual woman and facility level. Given the hierarchical structure of the data and variance in demand across facilities, we used a multilevel mixed-effect logistic regression to explore the determinants of facility-based delivery care. RESULTS: Eighty-six percent of 2846 women gave birth in a health facility. Demand for facility-based delivery care was influenced more by demand-side factors (76%) than supply-side factors (24%). On demand-side factors, facility births were more common among women who were educated, Muslim, wealthier, with their first childbirth, and those who had at least four antenatal care visits. On supply-side factors, facility births were more common in facilities offering outreach services, longer consultation times and higher interpersonal quality. In contrast, facilities with longer average waiting times, longer travel times and higher chances of charging delivery fees had few facility births. CONCLUSIONS: Policy responses should aim for strategies to improve demand like health education to raise awareness towards care seeking among less educated groups and those with higher parity, reduce financial barriers to access (including time costs to reach and access care), and policy interventions to enhance interpersonal quality in service provision.