Deletions of 22q11 cause DiGeorge sequence (DGS), velo-cardio-facial syndrome (VCFS), conotruncal anomaly face syndrome, and some isolated conotruncal heart anomalies. Demonstration of a 22q11 deletion in a patient with manifestations of DGS and Noonan syndrome (NS) has raised the question of whether NS is another of the chromosome 22 microdeletion syndromes. This prompted us to evaluate a cohort of patients with NS for evidence of 22q11 deletions. Five of 6 NS propositi studied in our laboratory with marker N25 (D22S75) did not have a 22q11 deletion. A 2-month-old infant with several findings suggestive of NS did have a 22q11 deletion, suggesting that a small number of 22q11 deletion propositi may present with a NS-like picture. However, most cases of NS must have another cause.