The aim of this study was to investigate the prevalence and associated risk factors of methicillin-susceptible and methicillin-resistant Staphylocccus aureus (MSSA and MRSA) carriage in care homes, with particular focus on dementia. A point-prevalence survey of 748 residents in 51 care homes in Gloucestershire and Greater Bristol was undertaken. Dementia was assessed by the clock test or abbreviated mini-mental test. Nasal swabs were cultured for S. aureus on selective agar media. Multivariable analysis indicated that dementia was not a significant risk factor for MSSA (16·2%) or MRSA (7·8%); and that residents able to move around the home unassisted were at a lower risk of MRSA (P=0·04). MSSA carriage increased with increasing age (P=0·03) but MRSA carriage decreased with increasing age (P=0·05). Hospitalization in the last 6 months increased the risk of MSSA (P=0·04) and MRSA (P=0·10). We concluded that cross-infection through staff caring for more dependent residents may spread MRSA within care homes and from the recently hospitalized. Control of MSSA and MRSA in care homes requires focused infection control interventions.