Pneumonia in patients in intensive care units (ICU) is associated with several diagnostic difficulties and high mortality. This study was conducted to describe the diagnostic procedures and clinical characteristics of the pneumonic and critically ill patient in relation to APACHE II score. The material consisted of 193 patients admitted to seven Danish ICUs and is also included in a European epidemiologic survey (EURO.NIS). Twenty-eight (14.5%) developed pneumonia and 18 (9.3%) of these were nosocomial (> 48h after admission). Patients with pneumonia had a significantly higher APACHE II score, duration of stay and mortality. The techniques used to diagnose pneumonia were mainly conventional and did not or only seldom include protected brush, bronchoalveolar lavage or pulmonary biosy. The predominant pathogens isolated in tracheal aspirate were Gram-negative bacilli (50%). The APACHE II scoring system was found to stratify patients with respect to mortality, duration of stay and pneumonia diagnosed in ICU.