Cancer of the bladder is a frequent malignancy in Egypt and other developing countries in which bladder infection with the parasite Schistosoma haematobium is common. Several epidemiological, histopathological, and clinical characteristics of cancer of the Bilharzial bladder suggest that it is distinct from bladder cancer seen in other places in the world. No numerical aberrations of chromosomes that might be specific for Bilharzial bladder carcinoma have been established. In this study, we used fluorescence in situ hybridization (FISH) with centromere-specific probes for chromosomes 3, 4, 7, 8, 9, 10, 11, 16, and 17 to detect numerical aberrations of these chromosomes in frozen-stored samples of 31 Egyptian patients affected with Bilharzial carcinoma. Among 5 types of chromosomes examined, imbalance was observed; the most common imbalance was a loss of chromosome 9 (48.4%), with numerical aberration of chromosome 17 being the second most-frequent anomaly (19.4%). The presence of such anomalies, especially losses of chromosome 9, are associated with a younger age group of patients, as well as with a lower grade tumor and negative pelvic node involvement by the disease. Fluorescence in situ hybridization analysis thus proved to be a useful method for detecting numerical aberrations of individual chromosomes, with application to touch preparations of frozen-stored tissue having the advantage of exact sampling of cancer foci. This result also suggests that the mechanism of genetic progression of bladder cancer is independent of its etiology.