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 absent in FHL patients. We report the first cases of familial hemophagocytic lymphohistiocytosis 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 mutation(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 hemophagocytic lymphohistiocytosis etiology in these cases.