Objective: To study routine surgical in-hospital care, and to relate postoperative morbidity and mortality to age, sex, tumour stage, operation done, and surgical workload of the hospital. Design: Prospective population-based study. Setting: All hospitals that diagnosed new cases of stomach cancer in five counties in central and northern Sweden, 1 February 1989-31 January 1995. Patients: All 1024 patients diagnosed as having a new adenocarcinoma of the stomach. Results: The stomach cancer was in such an advanced stage at diagnosis that only half of the patients could be offered a potentially curative operation. The tumour was resectable in 632 patients (62%). Distal gastric resection was done for 359 (57%) and total gastrectomy in 259 (41%) of all the resected cases. Postoperative complications occurred in 250 patients (31%). In multivariate analyses the relative risk (RR) for postoperative complications increased to 2.3 (95% confidence interval [CI] = 1.3 to 4.3) in patients over 79 years of age compared with those under 60. The corresponding RR for postoperative death was 5.1 (95% CI = 2.0 to 12.7) in patients over 79 years. Total gastrectomy combined with splenectomy and distal pancreatectomy carried the highest postoperative morbidity (RR = 3.3) and mortality (RR = 3.7) compared with distal gastrectomy. Conclusion: There was no difference in postoperative morbidity or mortality among different types of hospital categories. Surgical treatment of stomach cancer still carries a substantial morbidity and mortality in an unselected series of patients, particularly among elderly patients.