Review of the number of lung cancers subsequently developing in patients with chronic leukemia or lymphoma revealed a statistically significant (p less than .001) increase in the incidence of lung cancer in these patients. Of 684 patients with chronic leukemia seen between 1961 and 1972 (followed through 1976), 19 developed lung cancer versus 3 expected cases. Of 2708 patients with lymphoma seen in the same period, 23 developed lung cancer versus 7 expected cases. These data indicate that lung cancer be given serious consideration when a new pulmonary lesion is noted in these patients, and biopsy may be warranted.