The purpose of this study was to determine the effects of implant-overdenture treatment (IOT) on patients' complaints about dentures and the degree to which subjective treatment outcome could be predicted from baseline patient and treatment characteristics. Four groups of patients were distinguished: one pretreatment group, two posttreatment groups (1 year after treatment) and one reference group of denture wearers, who had not applied for any kind of treatment. They finished a questionnaire with 20 statements on denture complaints. Four scales concerning denture complaints could be distinguished and named after their underlying variables. Differences between the groups were analyzed. IOT treatment was shown to be very effective on a wide range of denture complaints. Little change was seen in patient satisfaction with regard to maxillary dentures when measured on the scales, although many patients wanted improvement in retention and stability for the maxillary denture after IOT treatment in the mandible. Sixteen percent of the denture wearers who had not applied for IOT expressed complaints regarding their mandibular dentures that matched or were more severe than those of the patients that had applied for IOT, before the actual start of treatment. Although generally the subjective treatment outcome of IOT was favorable, it could not be individually predicted from baseline patient and treatment characteristics.