The incidence of complicated pneumonia caused by S. pneumoniae is reported to be increasing. This increase may be related to host susceptibility and/or pathogen virulence. The objective of this study was to evaluate clinical and laboratory characteristics associated with complicated pneumococcal pneumonia, and to identify risk factors associated with prolonged fever and hospitalization. The study involved reviewing the records of all children who were hospitalized in four major hospitals in Jerusalem with a confirmed diagnosis of pneumococcal pneumonia during a 12-year period (1986-1997). Demographic, clinical, laboratory, and outcome variables were compared between those with uncomplicated and complicated pneumonia. One hundred and eleven children (median age, 2.2 years) were hospitalized with pneumococcal pneumonia during the study period. Forty-four (39%) of them had complicated pneumonia, characterized by pleural effusion, empyema, pneumothorax, pneumatocele, and/or atelectasis. There was no correlation between the isolation of penicillin-resistant S. pneumonia (16% of cases) and complicated pneumonia. Factors that were significantly associated with complicated pneumonia included weight <or=10% for age, respiratory distress (e.g., tachypnea, dyspnea), anemia, and a white blood cell count (WBC) <15,000/mm(3) at time of admission. Complicated pneumonia and a WBC <15,000/mm(3) on admission increased the risk for prolonged fever and an extended length of hospitalization. Based on these results, it is concluded that host factors such as anemia, low weight, and a low WBC are associated with complicated pneumonia. Both the presence of pulmonary complications and a relatively low WBC in children hospitalized for pneumococcal pneumonia are independent risk factors for protracted fever and extended hospitalization.