OBJECTIVES: To examine (i) the prevalence of comorbidity among invasive bladder cancer (IBC) patients, and (ii) the effect of comorbidity on IBC survival and mortality in Northern Denmark. Comorbidity has shown to be associated with treatment selection and survival in patients who undergo radical cystectomy for IBC. METHODS: Patients with a diagnosis of IBC from Danish hospitals between 1996 and 2007 within a population of 1.6 million were identified through the Danish National Patient Registry. From hospital diagnosis data, we computed Charlson Comorbidity Index scores (0, 1-2, 3+) for IBC patients and computed absolute survival and relative mortality estimates according to comorbidity level. RESULTS: We identified 3997 patients with IBC among whom 1715 (43%) had comorbidities. The prevalence of comorbidity tended to increase during the study period with those having scores 3+ increasing from 8%-12%. Three- and 5-year mortality rates were higher for patients with comorbidity, with mortality rates more than 2-fold higher among those with scores of 3+ and 1.5-fold higher among those with scores of 1-2 compared with no comorbidity. Generally, the same pattern was seen for 1-year relative survival rates. CONCLUSIONS: Comorbidity was seen among 43% of IBC patients and severe comorbidity was a predictor of poorer survival.