We conducted a noncurrent prospective study of all Olmsted County, Minnesota, residents who had had a lower-extremity venogram, pulmonary angiogram, or lung scan performed because of suspicion of deep venous thrombosis or pulmonary emboli. One hundred thirteen cancer-free patients were followed for 386 person-years from the date of procedure. Nine subsequent cancers were observed compared with 4.5 expected (relative risk, 2.0; 95% confidence interval, 0.9 to 3.8), using total cancer incidence rates for the Rochester, Minn, population. Five hundred seventeen cancer-free controls were followed for 2072 person-years. Twenty subsequent cancers were observed compared with 11.6 expected, yielding a relative risk of 1.7 (95% confidence interval, 1.1 to 2.7). When cases and controls were compared directly, no statistically significant difference in cancer-free survival was found.