Measuring the burden of cancer activity in big teaching multidisciplinary hospitals becomes a real challenge in France for organizational, quality of care and economic reasons. At the "Hospices Civils de Lyon" University Hospital in France, we have chosen to face this question by using the french DRG based information system called PMSI. It allows to identify hospital stays related to cancer care through the use of an algorithm based on selected ICD 10 codes for hospital stay. We then estimate the proportion of patients concerned by cancer and classify hospital stays and patients according to various epidemiological and clinical parameters. The results for the year 1999 taken as an example showed that 43,883 out of 293,827 (15%) of hospital stays were related with a diagnostic of cancer, corresponding to 12,777 different patients. The concordance study on 154 patients between the data from the electronic PMSI files and medical paper records showed a 97% concordance for cancer diagnosis and 93% for the precise type of tumor. In absence of hospital based cancer registries, the PMSI data base gives an accurate source of information for cancer burden and provides many potential applications in defining hospital policies for cancer management and resource allocations.