Evidence is scarce about the influence of comorbidity on outcome of surgery, whereas this information is highly relevant for estimating the surgical risk of cancer patients, and for optimising pre-, peri- and postoperative care. In this paper, the prognostic role of increasing age and comorbid conditions in patients diagnosed with stage I-III colorectal, stage I-II NSCLC or stage I-III breast cancer between 1995 and 2004 in the southern part of the Netherlands is summarised. Almost all patients with stage I-III colon cancer or rectal cancer underwent surgery regardless of age or comorbidity. In contrast, the resection rate among elderly patients with stage I-II NSCLC was clearly lower than among younger patients and was significantly lower when COPD, cardiovascular diseases or diabetes were present. Among patients with stage I-III breast cancer, those aged 80 or older underwent less surgery, and the resection rate appeared to be lower when cardiovascular diseases or diabetes were present. Among patients with resected colorectal cancer, postoperative morbidity and mortality were higher among those undergoing emergency surgery, and also among those with reduced pulmonary function, cardiovascular disease or neurological comorbidity. Among those with resected NSCLC, postoperative morbidity and mortality were related to reduced pulmonary function or cardiovascular disease. Since surgery for breast cancer is low risk, elective surgery, morbidity and mortality were not higher for elderly or those with comorbidity. Among patients with colorectal or breast cancer, comorbidity in general, cardiovascular diseases, COPD, diabetes (only colon and breast cancer) and venous thromboembolism had a negative effect on overall survival, whereas the effect of comorbidity on survival of stage I-II NSCLC was less clear. Elderly and those with comorbidity (especially cardiovascular diseases and COPD) among colorectal cancer and NSCLC patients had more postoperative morbidity and mortality. Prospective randomised studies are needed for refining selection criteria for surgery in elderly cancer patients and for anticipation and prevention of complications.