OBJECTIVE: Hospital-acquired pneumonia (HAP) is associated with high mortality and is the second most common nosocomial infection. The aim of this study was to calculate the incidence and to identify potential risk factors for HAP in an emergency ward for surgical patients admitted because of acute abdomen or trauma. DESIGN: A structured review of medical records was conducted. Patients diagnosed with pneumonia >48 h after admittance, were compared with a randomly chosen age-matched reference group. Ten variables judged as potential risk factors for HAP were studied in 90 patients. SETTING: An emergency ward for surgical patients with acute abdomen or trauma at an Univerity hospital in Sweden. PARTICIPANTS: A total of 90 patients with HAP and 120 age-matched controls were included. MAIN OUTCOME MEASURES: Risk factors for HAP in patients at a surgical clinic. RESULTS: Of a total of 10 335 admitted patients, during 4.5 years the hospital stay was longer than 48 h in 4961 patients. Of these 90 (1.8%) fulfilled the strict criteria for HAP. Potential risk factors were suspected or verified aspiration (odds ratio (OR): 23.9) that was 2-fold higher than immobilization (OR: 11.2). Further, chronic pulmonary obstructive disease (COPD)/asthma, abdominal surgery and gastric retention/vomiting were risk factors for HAP. CONCLUSION: Verified or suspected aspiration was the dominating risk factor for HAP but also immobilization was frequently associated with HAP. Various established preventive measures should be implemented in the nursing care to reduce the frequency of HAP.