Prostate cancer is the second most frequent cause of cancer death in males in Switzerland. Because the rate of prostate tumour growth varies from very slow to moderately rapid, one of the major challenges in the management/treatment of prostate cancer is the ability to reliably distinguish patients at risk of dying as a direct result of the disease from those more likely to die of other causes. The presence of other chronic diseases at the time of diagnosis affects the life expectancy of the patients, which, in turn, is – at least in theory – an important characteristic for treatment choice. Co-morbidity is defined as the co-existence of at least two chronic conditions or impairments in the same person. The Charlson co-morbidity index (CCI) is commonly used in longitudinal studies to classify co-morbid conditions that might alter the risk of mortality. It has previously been used to examine its predictive value for mortality after prostate cancer diagnosis, but these studies were often hospital-based, had a rather small sample size, or were restricted to specific sub-groups of prostate cancer patients. The Zurich Cancer Registry collects information from all cancer patients diagnosed who live in the Canton of Zurich; it is the largest registry in Switzerland with more than 6000 new cases per year, including 1000 prostate cancer cases and 220 prostate cancer deaths. For all prostate cancer cases diagnosed in 2000/2001, we aim to collect information on cancer diagnosis (including stage and grade) and treatment, co-morbidities, data of birth, place of residence, profession, body height and weight, smoking habits, and survival information. This information is partly routinely collected information from the cancer registry; other information has to be abstracted from records from the hospitals, in which the patients have been treated. We firstly aim at describing the prevalence and type of co-morbidities in all prostate cancer patients diagnosed in 2000 and 2001 who live in canton of Zurich, and then to examine the effect of co-morbidities on treatment choices in prostate cancer patients. The main aim is to examine the prediction of overall and prostate-cancer specific mortality by the presence of co-morbidities and whether this association is affected by the treatment of the tumor.