We describe 3 siblings with interleukin-12 receptor beta1 (IL-12Rbeta1) deficiency, a known genetic etiology of clinical disease caused by infection with poorly virulent mycobacteria, such as mycobacteria found in bacille Calmette-Guérin (BCG) vaccines and environmental nontuberculous mycobacteria (NTM). One child had disseminated tuberculosis, the second had extraintestinal salmonellosis and pulmonary tuberculosis, and the third remained asymptomatic. IL-12Rbeta1 deficiency should be considered as a diagnosis in patients with severe salmonellosis or tuberculosis, even if they do not have disease due to BCG or NTM.