Pneumocystis jirovecii pneumonia (PCP) in patients without AIDS is increasingly common. We conducted a prospective cohort study of consecutive patients with proven PCP; of 544 patients, 223 (41%) had AIDS (AIDS patients) and 321 (59%) had other immunosuppressive disorders (non-AIDS patients). Fewer AIDS than non-AIDS patients required intensive care or ventilation, and the rate of hospital deaths--17.4% overall--was significantly lower for AIDS versus non-AIDS patients (4% vs. 27%; p<0.0001). Multivariable analysis showed the odds of hospital death increased with older age, receipt of allogeneic bone marrow transplant, immediate use of oxygen, need for mechanical ventilation, and longer time to treatment; HIV-positive status or receipt of a solid organ transplant decreased odds for death. PCP is more often fatal in non-AIDS patients, but time to diagnosis affects survival and is longer for non-AIDS patients. Clinicians must maintain a high index of suspicion for PCP in immunocompromised patients who do not have AIDS.