Chromosomal 8p23 deletion syndrome is recognized as a malformation syndrome with clinical symptoms of facial anomalies, microcephaly, mental retardation, and congenital heart defects. The responsible gene for the heart defects in this syndrome has been identified as GATA4 on 8p23.1. Two patients with interstitial deletions of 8p23.1 were investigated; one patient showed moderate developmental delay and Ebstein anomaly, and the other showed mild delay and typical atrioventricular septum defect. The precise deletion sizes, 17 and 2.9 Mb, were determined by FISH analyses using BAC clones as probes. The latter deletion was the smallest deletion including GATA4 in the previously reported patients, and the critical regions and genes for clinical manifestation of 8p23 deletion syndrome, including facial anomalies, microcephaly, behavioral abnormality, and developmental delay, were discussed. © 2008 Wiley-Liss, Inc.