A further patient with the ICF syndrome (immunodeficiency, centromeric heterochromatin instability of chromosomes 1, 9 and 16 and facial anomalies) is described. This case is the second to be reported with consanguinity of the parents. This lends support to the theory of autosomal recessive inheritance. The features of the 15 published cases are reviewed. The clinical and cytogenetic characteristics of the syndrome are discussed, and new evidence provided as to the role of centromeres and centric heterochromatin in the production of chromosome aberrations. Correspondence with other authors has made possible a review of the clinical outcome in this condition.