In spite of the great value from the health planning point of view, only a few Cancer Registries have produced measures of prevalence. PREVAL is a computerized program for personal computers that provides prevalence data expressed as number or proportion. The program calculates prevalence, cross-classified by years from diagnosis and age. PREVAL reads data on the vital status, available from those Cancer Registries that have carried out population-based survival studies. Larynx cancer in males has been used as an example. Analysis has been performed on 15-year follow-up data of 840 incidence cases registered during 1976-1987 period from Lombardy Cancer Registry. In 1987, larynx cancer prevalence proportions are 67.6 per 100,000 for patients with up to 5 years from diagnosis and 108.4 per 100,000 for those with up to 10 years. The Authors will provide PREVAL free of charge upon request.