There are few data on Pneumocystis carinii pneumonia (PCP) in critically ill human immunodeficiency virus (HIV)-negative patients. Improved knowledge of the presenting symptoms of and prognostic factors for PCP may help to reduce the high mortality rate associated with PCP in such patients. We retrospectively studied 39 consecutive patients with acute PCP-related respiratory failure and malignancy who were treated at 2 intensive care units (ICUs) during a 10-year period. Univariate logistic regression identified the following 8 predictors of mortality at 30 days after patient admission to the ICU (30-day mortality rate, 33%): complete remission of the malignancy (odds ratio OR, 0.18), receipt of >1 course of antimalignancy chemotherapy (OR, 17.2), involvement of 4 lobes noted on a chest radiograph (OR, 5), >15% neutrophils in bronchoalveolar lavage BAL fluid specimens (OR, 6), Organ System Failure score (OR, 7.33), Simplified Acute Physiology Score II (OR, 1.12), and the need for either mechanical ventilation (OR, 63) or vasopressors (OR, 25.9). Studies are needed to determine whether aggressive monitoring and treatment of patients with >15% neutrophils in BAL fluid specimens can improve the outcome of critically ill patients with malignancy and PCP.