Microscopic residual tumour growth was found postoperatively in the bronchial resection lines in 44 out of a total of 1069 patients who underwent resection for pulmonary carcinoma. Bronchopleural fistula developed in six of these patients (13.6%). The incidence of bronchopleural fistula in the material overall was 4.2% (45 patients). Residual carcinoma therefore seemed to impair healing of the bronchial stump (p less than 0.01). Routine intraoperative frozen sections of the bronchial resection line can be recommended in order to reveal the residual carcinoma and thus lower the incidence of bronchopleural fistula. The five-year survival rate of these patients with microscopic residual carcinoma in their bronchial resection lines was similar to that in patients with the same TNM staging who had undergone resection for pulmonary carcinoma. Residual carcinoma in the bronchial resection line therefore did not worsen prognoses. The survival rate in our patients was better than survival rates reported for other series. Most of our patients had received postoperative radiotherapy. Previous reports relate to patients treated only surgically. Postoperative radiotherapy may therefore improve the prognosis in patients with residual tumour growth in their bronchial resection lines.