Cartilage-hair hypoplasia is an autosomal recessive osteo-chondrodysplasia which results in short stature, sparse hair and impaired cell-mediated immunity. In a study of 88 Finnish patients we found episodes of anaemia and/or macrocytosis during childhood in 86% of the patients. The reticulocyte index was always low in relation to anaemia. Bone marrow examination revealed decreased erythropoiesis in six of eight anaemic patients studied. Anaemia was most prevalent and severe during infancy. Spontaneous recovery occurred before adulthood in all patients except in three infants with fatal hypoplastic anaemia. Sixty-two percent of the patients had had lymphopenia and 24% neutropenia. Presence of anaemia significantly correlated to severity of immunodeficiency and growth failure and to presence of neutropenia. Disordered erythrogenesis is an integral feature of cartilage-hair hypoplasia and may, together with growth failure and immunodeficiency, reflect a generalized defect in cellular proliferation.