Twenty-three pediatric cancer patients developed Pseudomonas aeruginosa septicemia during an 11-year period. Typically the patients had advanced neoplasia and were receiving immunosuppressive therapy. Severe myelosuppression was almost always present and antibiotic therapy during the prior 2-week period for proven or suspected sepsis was common. Disruption of the skin and mucosa in the anogenital regions was evident in the majority of patients, and the gastrointestinal tract represented the most common portal of entry. Patients who developed sepsis while relapsed had the highest case-fatality rate, and use of synergistic antibiotic combinations did not affect outcome in this group.