The total medical costs of community-acquired pneumonia are directly related to the costs of hospital admission and length of stay. The aim of the present study was to evaluate the reasons for prolonged duration of stay in patients stratified in five risk classes for death, and to identify factors associated with prolonged stay. The study population consisted of 295 patients. According to lower (classes I, II, III) or to higher (classes IV, V) risk, the target duration of hospitalization was set at 5 and 7 days, respectively. The causes of prolonged hospitalization were classified as pneumonia-related, complications, unstable comorbid diseases and nonclinical factors. The overall percentage of patients with appropriate duration of hospitalization was 32%. Causes of prolonged hospitalization were related mainly to pneumonia (32%) from all risk classes. Morbid complications and instability of the underlying illness were greater in class V patients. Nonclinical factors were present in 29.5% of cases. Hypoxaemia, anaemia, hypoalbuminaemia, and complications appearing before 72 h were associated with prolonged hospitalization. The cause of prolonged hospitalization of patients with community-acquired pneumonia is multifactorial, depending mainly on pneumonia and comorbid conditions but there is a large number of unnecessary hospitalization days that could be reduced by improving the efficiency of hospital care.