An analysis is presented of 14 cases of diffuse mesothelioma [one of them involving the peritoneum, the rest being of the pleural type] in postmortem material for a period of 18 years [1962--1978] with a view to the clinical course, macroscopic and microscopic pictures, diagnostic possibilities, and to the relationship to aetiological factors. With only one exception, no correlation to asbestosis was found in terms of either the patients' personal histories or morphology. A meticulously performed postmortem examination appears to be the most reliable diagnostic criterion.