BACKGROUND: There are only inadequate studies on the characteristics of severe pneumonia in the patients who have solid cancer and who are treated with cytotoxic chemotherapy and also on the usefulness of the various severity index scores. METHODS: We retrospectively reviewed 31 patients who were treated with cytotoxic chemotherapy because of solid cancer and who were admitted to the medical ICU at Samsung Medical Center from April 2007 to August 2008. RESULTS: The median age of the 31 patients was 64 years old (34-79). The types of solid cancer were lung cancer (19, 61.3%), gastroesophageal cancer (4, 12.9%), breast cancer (2, 6.5%), liver cancer (1, 3.2%), ovarian cancer (1, 3.2%) and other types of cancer (4, 12.9%). The hospital mortality rate was 64.5%. We were able to determine the pathogen of 19 (61.3%) patients; S. pneumoniae (6), S. aureus (3), Candida species (3), P. aeruginosa (2), K. pneumoniae (1), Pneumocystis jiroveci (1) and others (3). There were no statistically differences of the laboratory data and severity index scores (PSI, CURB-65, APACHE II, SOFA, SAPS 3) between the survivors and nonsurvivors, except the P/F ratio. CONCLUSIONS: The hospital mortality rate of severe pneumonia in patients who had solid cancer and who received cytotoxic chemotherapy was high. The major pathogen was S. pneumoniae. The severity indexes for general pneumonia were not useful to these patients.