Seroma formation is the most common complication of a modified radical mastectomy for breast cancer. Postoperative wound seromas ocur in up to 53% of all patients undergoing mastectomies. We present a case who developed a seroma with a fibrous capsule after a modified radical mastectomy for breast cancer. The seroma was refractory to all conventional treatments,and required surgical resection. Altough seroma formation is the most frequent complication corelated with mastectomy and axillary dissection, seroma with fibrous capsule formation requiring surgical resection is a really rare antity. To our knowledge this is the second report of such a case. When lack of patient's life quality and serious morbidity of the complication considered, it seems to be important to diagnose early and perform maximum effort to prevent such complication with associate various methods.