A large epidemiological health investigation, the Helsinki Ageing Study (HAS), was performed in 1989-1991 in Helsinki, Finland. We report here the prevalence of oral mucosal lesions in 338 76-, 81- and 86-year-old home-living elderly people, who completed the oral health investigation at the Institute of Dentistry, University of Helsinki. One or more lesions were found in 128 subjects (38%). Fifty-one per cent of the edentulous complete-denture wearers and 31% of the elderly with some natural teeth had mucosal lesions. The most common finding was inflammation under the denture, which occurred alone or combined with other lesions in 25% of the denture wearers. The three most common mucosal changes not related to denture wearing were coated changes of the tongue (7%), angular cheilitis (6%) and varicose veins under the tongue (4%). No differences were found in the number of mucosal lesions among the three age groups. Angular cheilitis and inflammation under removable dentures were more frequent in women than in men. However, no other differences were found in the presence of mucosal lesions between sexes. The total number of mucosal lesions correlated positively with the number of medications used daily. Ninety-six per cent of the subjects with complete dentures, and 98% of those with some natural teeth reported cleaning their dentures at least once a day. Of the denture wearers, 88% reported cleaning their oral mucosa also, as part of their oral hygiene routine. The presence of mucosal lesions was related to self-reported cleaning of the denture-bearing mucosa. However, no association was observed between cleaning frequency and presence of mucosal changes.