The pathophysiology of seroma formation has yet to be determined. Therefore, the present study was undertaken to calculate the incidence of postoperative seromas after definitive breast cancer operations utilizing electrocautery dissection. Additionally, we attempted to identify risk factors associated with seroma development and to examine seroma formation in relation to operative procedure. A retrospective review of 252 breast cancer operations was undertaken. Patients were subdivided by operative procedure: modified radical mastectomy (MRM; n = 148), breast preservation with axillary node dissection (n = 64), or MRM with immediate reconstruction (n = 40). Electrocautery was used in development of skin flaps. Seromas developed in 39 of the 252 operations for an incidence of 15.5 per cent. Seroma formation was significantly lower in those patients receiving MRM with immediate reconstruction than in those receiving MRM (2.5% vs 19.6%; P = 0.009) and tended to be lower than for patients receiving breast preservation with axillary node dissection (14.06%; P = 0.052). Neoadjuvant chemotherapy was performed in 18 patients, of whom 6 developed seromas (P = 0.030). The incidence of postoperative seromas was low despite the use of electrocautery. An association of postoperative seromas with neoadjuvant chemotherapy was noted. Additionally, it appears that immediate reconstruction may reduce the incidence of postoperative seromas, presumably by filling the dead space in the chest wall.