The optimal tools for obtaining a diagnosis of dental agenesis (DA) among adults are childhood dental records and radiographs. However, these are often not available, and therefore the present study aimed to assess whether DA in adults could be validly assessed by self-reported information guided by a questionnaire. A questionnaire eliciting information on DA of permanent teeth was constructed, pilot-tested, and subsequently posted to a case group consisting of 334 young adults, for whom the DA status had been ascertained in the period from 1992 to 2002. A control group, consisting of 258 young adults randomly selected from the population from which the cases originated, was also approached with questionnaires. The response rate was 53.7% among cases and 46.4% among controls. The sensitivity and specificity of self-reported DA were estimated to be at least 0.88 (95% CI = 0.82-0.92) and 0.95 (95% CI = 0.89-0.98), respectively. These diagnostic test parameters are clearly inadequate for population-screening purposes. However, when screening patient groups with a higher occurrence of DA than is characteristic of the background population, the self-reported DA status may be a useful tool for identifying risk groups for conditions associated with the presence of DA.