We describe a family of three sisters affected by malignant mesothelioma (MM) (2 pleural and 1 peritoneal) and one brother affected by pleural plaques. All members of the family had been subjected to previous asbestos exposure of environmental-residential type. For 13 years, from 1951 to 1964, their housing was provided by the father's employer, an asbestos cement factory, and the factory warehouse was on the ground floor of the building they lived in. DNA extracted from paraffin-embedded MM samples was used to search for chromosomal alterations by a comparative genomic hybridization (CGH) method. In two cases, a loss at 9p was found to be the only change. The loss at 9p is a frequent event in malignant mesothelioma and the fact that this anomaly was diagnosed in two sisters as the only alteration suggests that this region may be the site of one or more oncosuppressor genes that could play an important role in the development of MM and in inducing greater genetic susceptibility to the carcinogenic effects of asbestos.