INTRODUCTION: Patients with inflammatory bowel disease (IBD) are predisposed to pneumococcal infections due to their underlying disease and iatrogenic immunosuppression. Vaccination with the 13-valent pneumococcal conjugated vaccine (PCV13) is recommended, but with poor take-up and few data available. We performed an open-label, phase IV, multicenter study to evaluate the safety and immunogenicity of PCV13 in adults with IBD and to analyze the influence of immunomodulating treatments on anti-pneumococcal seroresponses. METHODS: We enrolled 306 patients with IBD from March 2014 through February 2016, with the following exclusion criteria: current IBD flare, pregnancy, pneumococcal immunization in the previous 5 years, and influenza immunization in the previous 4 weeks. PCV13 was administered intramuscularly. Serotype-specific vaccine responses were evaluated using an opsonophagocytic assay. Adverse events were monitored by diary cards and standardized phone interviews. RESULTS: The median seroprotection rate increased significantly from 43.9% (95% confidence interval [CI], 42.3–45.5) at inclusion to 90.4% (95% CI, 89.5–91.3%; P < 0.001) after vaccination. Patients receiving anti–tumor necrosis factor agents achieved a slightly lower seroprotection rate (from 44.5% [95% CI, 42.3%–46.8%] to 86.6% [95% CI, 84.9%–88.1%]) than patients treated with other types of immunosuppressive regimens (thiopurine, methotrexate, oral corticosteroids; from 44.7% [95% CI, 41.7%–47.7%] to 93.8% [95% CI, 92.1%–95.2%]) or nonimmunosuppressive treatment (5-aminosalicylate, topical corticosteroids, vedolizumab; from 41.3% [95% CI, 37.9%–44.8%] to 95.2% [95% CI, 93.4%–96.6%]). There were no safety issues. DISCUSSION: Overall, the administration of PCV13 was highly immunogenic and well tolerated, irrespective of the baseline treatment, and should be encouraged in all adults with IBD.