INTRODUCTION: Seroma is a collection of serous fluid in the dead space of skin flaps or axilla following mastectomy. There have been various methods for preventing seroma, such as prolonged suction drainage, shoulder immobilization, reduction of dead place, among others. We present our experience on factors affecting seroma formation after mastectomy among West African patients. METHODS: this was a single centre prospective study conducted on consecutive female patients with breast carcinoma scheduled for mastectomy. Patients were recruited at the surgical outpatient clinic and data was collected using interviewer administered structured questionnaire which reflected the bio data, age, hypertension, diabetes and body mass index. Operative factors like type of mastectomy and instrument used in raising flaps were recorded. The drained fluid was emptied and recorded daily. The drain was removed when the amount became less than 50 mls over the previous 24 hours. Seroma was detected by clinical evaluation at day five or ten after removal of drain. RESULTS: sixty mastectomies were included in the study. The mean age of patients is 46.3±7.4 years. In evaluating the factors associated with seroma formation, we found that age of the patients, presence of hypertension, the type of surgery and instruments used for dissection has no effect on seroma formation. However, body mass index and fixing of flaps to pectoralis major directly affect seroma formation. CONCLUSION: age, hypertension and type of mastectomy have no effect on seroma formation after mastectomy.