Due to aging of the population the prevalence of both cardiovascular diseases (CVDs) and cancer is increasing. Elderly patients are often under-represented in clinical trials, resulting in limited guidance about treatment and outcome. This study gives insight into the prevalence of CVD among unselected patients with colon, rectum, lung, breast and prostate cancer and its effects on cancer treatment and outcome. Over one fourth (N = 11,200) of all included cancer patients aged 50 or older (N = 41,126) also suffered from CVD, especially those with lung (34%) or colon cancer (30%). These patients were often treated less aggressively, especially in case COPD or diabetes was also present. CVD had an independent prognostic effect among patients with colon, rectum and prostate cancer. This prognostic effect could not be fully explained by differences in treatment. Conclusions: Many cancer patients with severe CVD have a poorer prognosis. More research is needed for explaining the underlying factors for the decreased survival. Such research should lead to treatment guidelines for these patients. (C) 2009 Elsevier Ireland Ltd. All rights reserved.