Hemophagocytic lymphohistiocytosis (HLH) may develop secondary to infections, malignancies, immune deficiency syndromes, and rheumatologic and metabolic disorders. Associations between HLH and inborn errors of metabolism, including lysinuric protein intolerance, multiple sulfatase deficiency, galactosemia, Gaucher disease, Pearson syndrome, and galactosialidosis, have previously been reported in the literature. In this report the authors present 3 children with disorders of propionate metabolism--1 with methylmalonic acidemia and 2 with propionic acidemia--who developed secondary HLH during their metabolic attacks. All patients fulfilled the 5 HLH criteria of the Histiocyte Society. Familial HLH was ruled out by molecular analysis. Plasma exchange was performed for 2 of them. Unfortunately 1 died of multiorgan failure despite intensive therapy. This is the first report of such an association.