Although frequent, little is known about early-onset pneumonia that occurs in the postresuscitation period. Although induced hypothermia is recommended as a method of improving neurological outcome, its influence on the occurrence of early-onset pneumonia is not well defined. To describe the incidence, risk factors, causative agents, and impact on outcome of early-onset pneumonia occurring within 3 days after out-of-hospital cardiac arrest (OHCA). Retrospective analysis of a large cohort study of all patients successfully resuscitated after OHCA and admitted from July 2002 to March 2008 in two medical intensive care units (ICUs). Patients who presented accidental hypothermia or a known pneumonia before OHCA, or patients who died within the first 24 hours, were excluded. During this 6-year period, 845 patients were admitted after OHCA, and 641 consecutive patients were included. A total of 500 patients (78%) were treated with therapeutic hypothermia. In the first 3 days, 419 (65%) presented early-onset pneumonia. Multivariate analysis disclosed therapeutic hypothermia as the single independent risk factor of early-onset pneumonia (odds ratio, 1.90; 95% confidence interval, 1.28-2.80; P = 0.001). Early-onset pneumonia increased length of mechanical ventilation (5.7 ± 5.9 vs. 4.7 ± 6.2 d; P = 0.001) and ICU stay (7.9 ± 7.2 versus 6.7 ± 7.6 d; P = 0.001), but did not influence incidence of ventilator-associated pneumonia (P = 0.25), favorable neurologic outcome (P = 0.35), or ICU mortality (P = 0.26). After OHCA, therapeutic hypothermia is associated with an increased risk of early-onset pneumonia. This complication was associated with prolonged respiratory support and ICU stay, but did not significantly influence ICU mortality.