The prevalence of co-morbidity among elderly lymphoma patients is associated with a decrease in the use of chemotherapy. This study assessed the independent prognostic effect of co-morbidity in 1551 unselected lymphoma patients, diagnosed between 1995 and 2001 in the area of the population-based Eindhoven Cancer Registry. The prevalence of serious co-morbidity was 58% for patients with Hodgkin's disease (HD) who were over 60 years of age and 66% for patients with non-Hodgkin's lymphoma (NHL) who were over 60 years of age. The administration of chemotherapy declined in the presence of co-morbidity for elderly patients with early-stage HD and elderly patients with aggressive NHL. Co-morbidity was associated with a 10-20% decline in 5-year survival. Whether less frequent application of chemotherapy in the presence of co-morbidity is justified as far as complications, prognosis and quality of life are concerned requires further investigation.