We report the case of a boy with low expression of HLA class I molecules on peripheral blood mononuclear cells, which is associated with immunodeficiency. The patient, who had a Marfan-like phenotype, had chronic deep skin ulcers and sinobronchiectasis. Immunohistologic examination of the ulcerated skin showed a dense perivascular infiltrate composed of normal mature lymphocytes and macrophages. All cells in the infiltrate showed an apparently normal expression of HLA class I molecules, but intraepidermal dendritic Langerhans' cells were negative for CD1a, an antigen that is a highly specific marker for these cells and is abundantly expressed in some self-healing forms of cutaneous lesions. It is therefore speculated that a defective expression of CD1a molecules can contribute to the chronic persistence of deep skin ulcers, which have already been reported in association with defective expression of HLA class I molecules.