The proportion of elderly cancer patients has increased considerably. This means that more patients are being diagnosed with one or more serious concomitant condition which may complicate the treatment of cancer. Little is known about treatment outcomes, as elderly patients with comorbidity are often excluded from clinical trials. The Eindhoven Cancer Registry has been registering serious co-morbidity in North-Brabant and North-Limburg in the Netherlands since 1993. Using data from patients diagnosed with cancer in 1995-2001, the correlation between age and comorbidity and choice of therapy and survival rates was described. Very elderly patients or patients with co-morbidity often were not treated in accordance with the guidelines. Elderly patients with localized lung cancer or prostate cancer underwent less surgery as often and elderly patients with colorectal cancer, breast cancer or ovarian cancer received less adjuvant chemotherapy or radiotherapy than younger patients. The prognosis was often worse for elderly patients than for younger patients, and the presence of co-morbidity decreased survival in most types of tumour. The question remains whether the prognosis for elderly patients with cancer would improve if more of them were treated in accordance with the guidelines, or if this will only lead to more complications.