Health gains oftentimes associated with income growth have been stubbornly slow in Nigeria in the past 25 years. One plausible reason for this stagnation is underperformance in the country's primary health care (PHC) system. The Primary Health Care Performance Indicators conceptual framework is used to examine Nigeria's PHC system and possible causes of underperformance. Analysis was conducted using a variety of sources including recent facility level information from the World Bank Service Delivery Indicators Survey. Results show that Nigeria has a relative abundance of PHC centers, reasonable geographic access to PHC, and relatively high health worker density. However, the performance of the PHC system is hindered by (1) segmented supply chains; (2) a lack of financial access to PHC; (3) a lack of infrastructure, drugs, equipment, and vaccines at the facility level; and (4) poor health worker performance. Altogether, these factors reflect two overarching system-level challenges—financing and governance—that are key root causes of the dysfunctions observed in the PHC system in Nigeria. Compared with peer African countries, Nigeria ranks low on nearly all PHC performance indicators. The government has taken important steps to address these root causes of underperformance, but policy gaps remain in achieving sustainable and equitable provision of PHC for the people of Nigeria.