An increased occurrence of complicated parapneumonic effusions in children has been reported from the UK and USA. Data from mainland Europe are scarce. We investigated the incidence of complicated parapneumonic effusion and empyaema in children admitted to the University Hospital of Leuven between 1993 and 2005, an era when pneumococcal conjugated vaccination had not yet been implemented. Sixty-eight cases were identified. The incidence increased from 20-55/100,000 hospital admissions to 120-130/100,000 hospital admissions in 2005, with 50% of the cases occurring from 2003 onwards (late cohort). This increase occurred later than that reported in the UK and US, but is of similar magnitude. The median patient age was 3.6 years (range 0.5-17 years). The median duration of symptoms before admission was 4 days (quartile values 3-7 days). The median white blood cell (WBC) count was 15,450 WBC/mm3 (quartile values 11,300-21,200 WBC/mm3) and the median C-reactive protein (CRP) level was 242 mg/L (quartile values 143-344 mg/L). Patients in the late cohort seemed to have worse disease compared to early cohort patients; significantly higher pleural lactate dehydrogenase (LDH) level (P = 0,02), higher pleural WBC, lower pleural glucose level and significantly longer duration of hospitalisation in the later cohort (P < 0,05), possibly reflecting more severe disease. In both cohorts, Streptococcus pneumoniae was the most frequently isolated pathogen, with serogroup 1 prevailing. The occurrence of complicated parapneumonic effusion increased in Belgian children before pneumococcal vaccination was added to routine childhood immunisations. This increase is pronounced from 2003 onwards (late cohort) and, thus, occurred later than that reported in the UK and USA; several parameters point towards the occurrence of more serious disease in the late cohort patients.