DiGeorge syndrome (DGS) is predominantly caused by partial monosomy 22q11, but a subset of patients with DGS show deletions of 10p or other chromosomal abnormalities. The authors describe a 20 months old girl with DGS and a monosomy 10p bringing the number of DGS patients with this chromosomal abnormality to nine. She has a monosomy 10p13-pter and a trisomy 10q26-qter due to a meiotic recombination of a maternal inversion (10) (p13q26). The proposita's phenotype demonstrates typical features of the del (10p) syndrome which include mental retardation, abnormally shaped skull, hypertelorism, low nasal bridge, micrognathia, dysmorphic low set ears, short neck, foot abnormalities, and cardiac defect. The diagnosis of DGS was made unequivocally within the first weeks of life because of the typical features-cardiac defect, hypoplastic thymus, T-cell defect, hypocalcemia, and hypoparathyroidism. The common DGS mutation-microdeletion 22q11-was excluded by FISH analysis, and the breakpoints on chromosome 10 were mapped between D10S189 and D10S191 on the short arm and proximal to D10S25 on the long arm.