A 4-year experience with Legionella pneumophila (LD) diagnosed in 36 patients with cancer was reviewed. Cancer patients represented 24% of the total population of patients acquiring LD during that time. Hematologic neoplasms (42%) and lung cancer (22%) accounted for the majority of afflicted patients. Nosocomial infections occurred in 42% of the patients evaluated. Several risk factors were assessed, and only neutropenia, and previous steroid therapy played a causal role (p less than .05) when assessed in a retrospective case control fashion. Overall mortality in oncology patients with LD (53%) was high and underscores the need rapidly to diagnose and treat this entity. This mortality decreased after 1977 when an effective antibiotic was utilized. Mixed infections also played a major role in outcome and occurred in 31% of the 36 patients studied. The mortality in these cancer patients was 73%, and this emphasizes the need to exclude and treat concomitant bacterial or fungal infections.