Nineteen children with hemophagocytic lymphohistiocytosis (HLH) were studied in the Department of Pediatric Hematology, Hacettepe University. Patients were divided into two groups. Group 1: Thirteen patients were classified as having a genetic etiology (7 familial, 6 presumed familial) on the basis of an affected sibling and consanguinity. There was a history of consanguineous marriage in 13 of the families. Seven of them had a history of a sibling with HLH. Group 2: Six patients were diagnosed with sporadic HLH. The age at presentation for familial patients was 0.7-84 months (mean 21.9 +/- 24.9 months), and for sporadic cases it was 2.5-48 months (mean 22.7 +/- 19.8 months). The clinical and laboratory data of these two groups were similar at diagnosis. Thirteen cases were diagnosed premortem by bone marrow aspiration. Splenic biopsy was performed in 2 patients. Four patients were diagnosed by postmortem examination. Elevated LDH levels were found in all patients tested. No significant differences for clinical and laboratory data were found between the two groups.