Perforin gene (PRF1) mutations have been reported in 20-30% of patients with familial hemophagocytic lymphohistiocytosis (FHL), an immune disorder of infancy and early childhood. Cytotoxic T and natural killer (NK) cell activities are remarkably reduced or ab-sent in FHL patients. We report the first cases of familial hemophagocytic lymphohistiocy-tosis in an Iranian family with two siblings. Exons 2 and 3 of the PRF1 gene were analyzed by polymerase chain reaction (PCR) amplification and direct sequencing. Perforin gene mu-tation(s) were detected in none of the cases. The result of our study indicates that not much evidence is present concerning a correlation between perforin gene defects and familial he-mophagocytic lymphohistiocytosis etiology in these cases.