Çekiç Ş, Özgür T, Karalı Y, Özkan T, Kılıç SŞ. Vedolizumab treatment in a patient with X-linked agammaglobulinemia, is it safe and efficient? Turk J Pediatr 2019; 61: 937-940. The loss of inflammatory regulation resulting from the absence of B-lymphocytes leads to a risk for autoimmune and autoinflammatory complications. There is no data on the use of Vedolizumab in patients with X-linked agammaglobulinemia (XLA) as well as children with another primary immunodeficiency (PID) diseases. A 4-year-old boy was admitted to our clinic with a history of recurrent respiratory tract infections. He was diagnosed with XLA based on extremely low immunoglobulins, very low level of B cells, genetic mutation of BTK gene, and family history. At the age of 8, he suffered from intermittent fever attacks, abdominal pain, weakness, oral aft, and weight loss. His clinical and laboratory features were consistent with inflammatory bowel disease. Histopathological examination of the biopsy material obtained from terminal ileum, colon and cecum showed Crohn`s disease. Initially, he was treated with prednisolone and infliximab. Because of the lack of response, infliximab treatment was switched to adalimumab. Terminal ileum was resected to relieve obstruction complication. Although he had been treated with adalimumab, a significant improvement was not observed. Vedolizumab (Entyvio™), a humanized monoclonal antibody α4β7 integrin-receptor antagonist, was commenced. After treatment with vedolizumab, his fever and abdominal pain attacks reduced, his total daily calorie intake increased and weight gain improved. He began to walk again and continued his school education properly. No side effects were observed in 18 months. This is the first immunocompromised child treated with vedolizumab. The symptoms of the patient receded and no side effect were seen during the treatment.