BACKGROUND: Little information is available on the influence of comorbidities on outcomes of older patients with acute pancreatitis. This study aimed to investigate the influence of comorbidities on outcomes of older patients with acute pancreatitis using data from a national Japanese administrative database. 
METHODS: A total of 14 322 older patients (≥70 years) with acute pancreatitis were referred to 1090 hospitals between 2010 and 2012 in Japan. We collected patients' data from the administrative database to compare the in-hospital mortality and length of stay of older patients with acute pancreatitis. The patients were categorized into four groups according to comorbidity level using the Charlson Comorbidity Index (CCI): none (CCI score=0; n=6890); mild (1; n=3874); moderate (2; n=2192) and severe (≥3; n=1366). 
RESULTS: Multiple logistic and linear regression analyses revealed that severe comorbidity was significantly associated with higher in-hospital mortality and longer length of stay [odds ratio (OR)=2.26; 95% confidence interval (CI): 1.75-2.92, P<0.001 and coefficient 4.37 days; 95% CI: 2.89-5.85, P<0.001, respectively]. In addition, cardiovascular and renal diseases were the most significant comorbidities affecting outcomes of the older patients. ORs of cardiovascular and renal diseases for mortality were 1.44 (95% CI: 1.13-1.85, P=0.003) and 2.69 (95% CI: 1.88-3.85, P<0.001), respectively, and coefficients for length of stay were 3.01 days (95% CI: 1.34-4.67, P<0.001) and 3.72 days (95% CI: 1.01-6.42, P=0.007), respectively. 
CONCLUSION: This study demonstrated that comorbidities significantly influenced outcomes of older patients with acute pancreatitis and cardiovascular and renal comorbidities were significant factors affecting outcomes.