A retrospective study of 38 patients with propionic acidemia indicates a high frequency of infections; affecting 80% of such patients. The Saudi Arabian population studied is a product of consanguineous marriages, and presents with a severe phenotype. Most microorganisms implicated are unusual, which suggests an underlying immune deficiency. These frequent infections occur despite aggressive treatment with appropriate diets, carnitine and during acute episodes of the disease with metronidazole, which suggests a global effect of the disease on T and B lymphocytes as well as on the bone marrow cells. Any patient with propionic acidemia should be closely followed up for an intercurrent infection in association with acute metabolic decompensation.