Prevalence of malignant neoplasm is a basic health indicator used in order to evaluate needs in medical equipment for treatment and follow-up of cancer patients. Data on prevalence are regularly published by Northern European countries. Thames and Connecticut cancer registries. In France available information on prevalence are scanty, because follow-up of cancer patients is not easy. Therefore, we used a statistical method to evaluate prevalence from incidence and mortality in the Rhône-Alpes area (France, 5,300,000 inhabitants) in 1990, using the department of Isère population based registry. For females, figures for breast carcinoma and colorectal carcinoma are respectively 25,000 and 5,700, and, for males, 5,700 colorectal carcinoma. For 5 year partial prevalence, these figures are respectively 11,300, 3,100 and 3,500. The ratio prevalence/incidence is 8.9 for breast in females, 5.8 for colorectal carcinoma in females and 4.8 for colorectal carcinoma in males with a steep decrease for 5 year partial prevalence (4 for breast carcinoma, 3.1 for females colorectal carcinoma and 2.9 for males colorectal carcinoma). These ratios are consistent with those observed elsewhere in Europe.