Natalizumab is a humanised monoclonal antibody targeting the lymphocyte adhesion molecule a4 integrin, with proven efficacy in multiple sclerosis (MS) and Crohn's disease (CD). The development of sarcoidosis with extrapulmonary involvement is reported in two patients with refractory CD who had received maintenance therapy with natalizumab. This complication has not been previously reported. It is hypothesised that the effect of natalizumab in altering lymphocyte mucosal trafficking may underlie the development of sarcoidosis in these patients.