The impact of comorbid diseases on ovarian cancer survival is largely unknown. We therefore examined (i) the prevalence of comorbidity among ovarian cancer patients and (ii) the impact of comorbidity on ovarian cancer survival and mortality. Using hospital discharge data, we identified Danish women diagnosed with ovarian cancer between 1995 and 2005 (n= 1995 within a population of 1.6 million) and then computed Charlson comorbidity index scores (0, 1-2, and 3+). We estimated the prevalence of comorbidity and computed absolute survival and relative mortality rate ratios (MRRs) according to comorbidity level, using patients with Charlson score 0 as the reference group. During the study period, the proportion of patients without comorbidity fell from 81% to 75%, while the proportion of patients with comorbidity score 1-2 and 3+ rose from 16% to 21% and from 4% to 5%, respectively. Overall 1-year survival increased from 68% in 1995-1997 to 70% in 1998-2000 and to 73% in 2001-2004. For patients with Charlson score 1-2, 1-year adjusted MRRs were 1.1 (95% CI, 0.8-1.6) in 1995-1997, 1.3 (95% CI, 1.0-1.8) in 1998-2000, and 1.7 (95% CI, 1.3-2.4) in 2001-2004. For patients with Charlson score 3+, 1-year adjusted MRRs were 2.4 (95% CI, 1.4-4.3) in 1995-1997, 1.6 (95% CI, 1.0-2.7) in 1998-2000, and 2.2 (95% CI, 1.3-3.8) in 2001-2004. The 5-year MRRs were similar to the 1-year MRRs. One quarter of Danish women with ovarian cancer were found to have comorbid conditions, and 5% had severe comorbidity. Severe comorbidity was a predictor of poorer survival.