Understanding the level, trend, geographical variations and determinants of use of modern family planning (FP) plays a major role in designing effective interventions leading to increased usage. This study assessed these characteristics of FP use in Nigeria using data from the 2003, 2005 and 2007 National HIV/AIDS and Reproductive Health Survey, a national population-based household survey. A Bayesian geo-additive procedure was used, which provides flexible modelling of non-linear and spatial effects at a highly disaggregated level of states. The findings reveal considerable geographical variation in the use of modern FP in Nigeria, with a distinct north–south divide. Furthermore, a significant trend in the use of modern FP was evident, with an increase between 2003 and 2005 followed by a decline between 2005 and 2007. The effect of respondent's age was non-linear, and use of modern FP was found to differ significantly between never-married and currently/formerly married respondents. Awareness of FP methods and knowledge of where to get/buy FP services/methods were found to be significantly associated with usage. The findings provide policymakers with tools to prioritize the use of scarce resources for implementing FP and reproductive health interventions.