A girl with severe neonatal hypocalcaemia, thymic hypoplasia, congenital heart disease and mental retardation in combination with a partial monosomy of chromosome 22, del(22)(pter-q11.3), is reported. Nine other patients with an association between partial monosomy 22 and a DiGeorge syndrome have been reported earlier, and this combination probably constitutes a deletion syndrome similar to the Prader-Willi and the aniridia-Wilms' tumour syndromes. However, the deletion of chromosome 22 is mostly due to a translocation, with trisomy for another chromosomal segment. Such a mechanism may explain the different clinical features seen in patients with partial monosomy 22. In the present case there was an unbalanced translocation with a probable trisomy of the short arm of chromosome 20 combined with the partial monosomy 22. Cytogenetic investigation with high resolution banding techniques is indicated in patients with thymic aplasia and suspected DiGeorge syndrome.