Perforin gene (PRF1) mutations have been reported in 20-30% of patients with familial hemophagocytic lymphohistiocytosis (FHL), an autosomal recessive disorder of infancy and early childhood that impairs or abolishes lymphocyte cytotoxicity. We report the first case of FHL in an adult patient homozygous for A91V in PRF1 with tuberculosis. The monozygotic twin of the patient is healthy. A91V confers genetic susceptibility for the development of FHL, but is not enough to trigger the disease on its own. We discuss the role of the A91V change together with M. tuberculosis infection as synergistic factors in the late onset of FHL.