Summary Estimates of maternal mortality are crucial to inform the planning of reproductive health programmes and guide advocacy. The aim of this study was to obtain a population-based estimate of maternal mortality in Lagos State, Nigeria. The sisterhood method was used in 2008 to carry out the survey using a questionnaire in which respondents were asked about their sisters who died during pregnancy, childbirth or within 6 weeks after childbirth. The survey involved 4,315 respondents who provided information on 9,910 ever married sisters. The life-time likelihood (risk) of maternal death for women aged 15-49 years was found to be 0.0239 or 1 in 42. The estimated maternal mortality ratio was 450 per 100,000 live births with a 95% CI of 360 and 530. Out of 111 reported deaths, 35 (31.5%) occurred during pregnancy, 49 (44.1%) occurred during delivery and 27 (24.3%) within 6 weeks of delivery.