In evaluating recurrent childhood infections, the physician must keep in mind the rarity of true immunodeficiency and the frequency of atopy, day care, exposure to cigarette smoke and anatomic variations as predisposing factors in recurrent childhood illnesses. Determining true immunodeficiency involves exclusion of risk factors for human immunodeficiency virus infection, identification of a family history of immunodeficiency and recognition of specific physical and laboratory findings. In most cases, screening immunoglobulin studies will distinguish the normal child from the child with an abnormal immune system. Management of the patient with true immunodeficiency is carried out in collaboration with specialists in these uncommon disorders.