Only 2 small population-based studies have previously evaluated cancer risk in splenectomized patients. Our objective was thus to investigate cancer incidence following splenectomy for external trauma or for surgical treatment of non-malignant conditions of adjacent organs. Using the unique personal identification number assigned to each Swedish resident, we linked centralized hospitalization records with nationwide total population and cancer incidence data. We excluded cancers diagnosed within the first 12 months after splenectomy and computed standardized incidence ratios for 1,295 patients (contributing 14,390 person-years) splenectormized for external trauma and for 985 patients (contributing 8,91 1 person-years) whose splenectomy accompanied surgical treatment of non-malignant conditions of adjacent organs (mostly peptic ulcers), using age-, sex- and period-specific rates for cancer incidence derived from the entire Swedish population. Patients undergoing splenectomy for external trauma had no significant excess of total or site-specific cancers. Individuals splenectormized in conjunction with surgery for non-malignant conditions of adjacent organs had a non-significant 40% elevated risk of total cancer, with significant increases of lung and ovarian cancers. The excesses of lung and ovarian cancers may be due to chance, but we could not exclude the conditions for which the surgery was performed, other treatments or common predisposing factors (such as cigarette smoking, which has been linked with both peptic ulcer and lung cancer).