A 25 year longitudinal study was carried out on a number of patients fitted with removable partial dentures (RPDs) in 1969. Before the prosthetic treatment all patients were given oral hygiene motivation and instructions in order to create a high level of co-operation. The RPDs, most of which were lower bilateral distal extension dentures, were carefully planned and designed. During the first 10 years the patients were examined in our clinic at yearly intervals at which time encouragement and reinstruction regarding oral hygiene were given and various treatment procedures were performed as required. After the initial 10 years the patients were advised, for practical reasons, to continue to have yearly controls on their own initiative. Of the initial 30 patients from 1969, 23 were still alive in 1994, all of whom were examined. In five of those 23 the original RPD situation had changed more or less due mainly to general illness contracted and/or change to other therapies. In the remaining 18 patients wearing in total 20 RPDs, 13 (65%) of the original RPDs were still functioning. Seven RPDs were new with principally the same design as the original ones. Among these 18 patients the number of lost teeth, the number of new DF surfaces and the increased number of endodontically treated teeth were few. No apparent changes took place regarding the periodontal condition during the follow-up period.(ABSTRACT TRUNCATED AT 250 WORDS)