PURPOSE: Advanced stage at diagnosis is a common feature of breast cancer in Sub-Saharan Africa (SSA), contributing to poor survival rates. Understanding its determinants is key to preventing deaths from this cancer in SSA. METHODS: Within the Nigerian Integrative Epidemiology of Breast Cancer Study, a multicentred case-control study on breast cancer, we studied factors affecting stage at diagnosis of cases, i.e. women diagnosed with histologically confirmed invasive breast cancer between January 2014 and July 2016 at six secondary and tertiary hospitals in Nigeria. Stage was assessed using clinical and imaging methods. Ordinal logistic regression was used to examine associations of sociodemographic, breast cancer awareness, health care access and clinical factors with odds of later stage (I, II, III or IV) at diagnosis. RESULTS: A total of 316 women were included, with a mean age (SD) of 45.4 (11.4) years. Of these, 94.9% had stage information: 5 (1.7%), 92 (30.7%), 157 (52.4%) and 46 (15.3%) were diagnosed at stages I, II, III and IV, respectively. In multivariate analyses, lower educational level (odds ratio (OR) 2.35, 95% confidence interval: 1.04, 5.29), not believing in a cure for breast cancer (1.81: 1.09, 3.01), and living in a rural area (2.18: 1.05, 4.51) were strongly associated with later stage, whilst age at diagnosis, tumour grade and oestrogen receptor status were not. Being Muslim (vs. Christian) was associated with lower odds of later stage disease (0.46: 0.22, 0.94). CONCLUSION: Our findings suggest that factors that are amenable to intervention concerning breast cancer awareness and health care access, rather than intrinsic tumour characteristics, are the strongest determinants of stage at diagnosis in Nigerian women.