During 1997-2004, microbiologically confirmed gastrointestinal infections were reported for 101,855 patients in Sweden. Among patients who had Salmonella infection (n = 34,664), we found an increased risk for aortic aneurysm (standardized incidence ratio [SIR] 6.4, 95% confidence interval [CI] 3.1-11.8) within 3 months after infection and an elevated risk for ulcerative colitis (SIR 3.2, 95% CI 2.2-4.6) within 1 year after infection. We also found this elevated risk for ulcerative colitis among Campylobacter infections (n = 57,425; SIR 2.8, 95% CI 2.0-3.8). Within 1 year, we found an increased risk for reactive arthritis among patients with Yersinia enteritis (n = 5,133; SIR 47.0, 95% CI 21.5-89.2), Salmonella infection (SIR 18.2, 95% CI 12.0-26.5), and Campylobacter infection (SIR 6.3, 95% CI 3.5-10.4). Acute gastroenteritis is sometimes associated with disease manifestations from several organ systems that may require hospitalization of patients.