PURPOSE Mastectomy without reconstruction is recommended for most Nigerian women with non-metastatic breast cancer (BC), but only 43% receive surgery, partly due to psychosocial factors. Patient-reported outcome measures (PROMs) are valuable tools for improving patient-centered care. BREAST-Q is a validated PROM for evaluating satisfaction and health-related quality of life after BC surgery. This research aimed to measure the effect of mastectomy on PROMs across BC stages in Nigeria, using BREAST-Q for the first time in this setting. METHODS A psychometrically validated, Yoruba version of the BREAST-Q mastectomy module was administered pre-operatively and at multiple time-points post-operatively to Nigerian women with non-metastatic BC undergoing mastectomy at three academic institutions. Domains: psychosocial well-being, physical well-being chest, sexual well-being and satisfaction with breasts, had both pre-and post-operative applicability. BREAST-Q scores were transformed into RASCH equivalents (0=worst, 100=best). Differences between scores pre-operatively and at 6-months post-operatively were compared using a paired t-test within early-stage (I/II) and late-stage (III) cohorts. RESULTS 108 patients had a median age of 50 (IQR 43, 59). 102 had documented stage: I–5 (5%), II–42 (41%), and III–55 (54%). 90 (83%) received neoadjuvant chemotherapy. 12 (11%) received post-mastectomy radiation. Mean pre-operative BREAST-Q scores across all domains were lower for early- vs. late-stage disease. Patients with early-stage BC had significantly higher mean BREAST-Q scores at 6-months post-operatively than pre-operatively in three of four domains: psychosocial well-being (pre-op: 60/post-op: 67, p-value=0.024), physical well-being chest (pre-op: 13/post-op: 27, p-value<0.001), and satisfaction with breasts (pre-op: 55/post-op: 65, p-value=0.031). Sexual well-being was not significantly different between time-points (pre-op: 29/post-op: 24, p-value=0.3). In patients with late-stage BC, psychosocial well-being (pre-op: 66/post-op: 67, p-value=0.6), physical well-being chest (pre-op: 22/post-op: 20, p-value=0.5), and satisfaction with breasts (pre-op: 58/post-op: 52, p-value=0.13) scores were similar pre- and 6-months post-operatively. Sexual well-being decreased significantly at 6-months (pre-op: 42/post-op: 25, p-value<0.001). CONCLUSION We report the first-ever use of the BREAST-Q in Nigeria. PROMs following mastectomy were unchanged or better in most domains. Significant improvement was seen in patients with early-stage disease. These results can inform pre-operative patient counseling to guide expectations and reduce fear. Interventions to improve sexual well-being are needed for patients with late-stage disease.