Norovirus outbreaks occur worldwide every year and have become more frequent over the last few years. There were extensive outbreaks in Hong Kong from May to July 2006 and our aim was to describe nosocomial outbreaks from 1 May 2006 to 31 July 2006 in this retrospective observational study. A total of 38 confirmed norovirus outbreaks involving 218 patients were identified. Most of these patients were elderly with a mean age of 74.5 years (range: 3 months to 97 years); 62% of them were either totally or partially dependent for help with daily activities, 83.9% had underlying chronic medical problems and 56% had limited mobility. In all, 97.2% of individuals presented with diarrhoea and only 46.3% of them had vomiting. The median duration for diarrhoea was 3 days and the longest 24 days. The median duration of vomiting was one day and the longest 15 days. Fever occurred in one-third of all cases. Reverse transcriptase-polymerase chain reaction was positive for norovirus in 72.6% cases. We conclude that nosocomial norovirus infection often involves frail elderly patients with limited mobility and that these patients may have more prolonged symptoms.