Significance Mendelian susceptibility to mycobacterial disease (MSMD) is defined by selective vulnerability to weakly virulent mycobacteria. The 32 known inborn errors of IFN-γ immunity account for MSMD in about half of the patients, and for a smaller proportion of cases of tuberculosis (TB). We report homozygous ZNFX1 variants in two families in which the index cases had MSMD or TB with intermittent monocytosis. Upon overexpression, the two variants encode truncated proteins. We show that human ZNFX1 is localized in ribonucleoprotein granules called stress granules. The patients’ production of and response to IFN-γ are apparently intact, and the patients have not experienced severe viral illnesses. Inherited deficiency of stress granule-associated ZNFX1 is a genetic etiology of MSMD or TB with intermittent monocytosis.