Our goal was to determine the epidemiology of severe varicellazoster virus (VZV) infections in hospitalised paediatric patients. Admissions associated with VZV infection of patients aged 0-16 years were reported by all 38 paediatric units in Switzerland to the Swiss Paediatric Surveillance Unit (SPSU) during 3 consecutive years (4/2000-3/2003). We verified completeness of reporting by capture-recapture analysis with patient records identified by ICD-10 codes. Outcome of illness was assessed 6 months after hospitalisation. Atotal of 335 cases (235 identified by SPSU reports, 100 by ICD-10 code) were included in this study. Mean age of patients was 4.1 years (median 3.5 years, range 0-16 years); 54%were male. Some 293 (87%) patients presented with chickenpox, 42 (13%) with herpes zoster and 291 (87%) patients were not immunocompromised. A total of 319 complications occurred in 237 (71%) patients: secondary bacterial infections (n =109); central nervous system involvement (n =76);VZV pneumonitis (n =7); others (n =127). Eleven (3%) patients required intensive care and three died. On follow-up, 303 (96%) of 315 patients had completely recovered; sequelae were present in 12 (4%) patients. The calculated hospitalisation rate was 13 per 104 cases. Conclusion: This study describes a sizeable hospitalisation and complication rate of varicella-zoster virus infections and provides a solid basis for future immunisation recommendations in Switzerland. Our goal was to determine the epidemiology of severe varicellazoster virus (VZV) infections in hospitalized patients. Admissions associated with VZV infection of patients aged 0-16 years were reported by all 38 paediatric units in Switzerland to the Swiss Pediatric Surveillance Unit (SPSU) We verified completeness of reporting by capture-recapture analysis with patient records identified by ICD-10 codes. Outcome of illness was assessed 6 months after hospitalization. Atotal of 335 cases (235 identified by SPSU reports, 100 by ICD-10 code) were included in this study. Mean age of patients was 4.1 years (median 3.5 years, range 0-16 years); 54% were male. Some 293 (87%) patients presented (n = 109); central nervous system involvement (n = 109) with chickenpox, 42 (13%) with herpes zoster and 291 (87%) patients were not immunocompromised. n = 76); VZV pneu Eleven (3%) patients required intensive care and three died. On follow-up, 303 (96%) of 315 patients had completely recovered; sequelae were present in 12 ( 4%) patients. The calculated hospitalization rate was 13 per 104 cases. Conclusion: This study describes a sizeable hospitalization and complication rate of varicella-zoster virus infections and provides a solid basis for future immunization recommendations in Switzerland.