Noonan syndrome is a multiple congenital anomaly condition characterized by craniofacial anomalies, short stature, cardiac malformations, and normal peripheral blood karyotype analysis. Prior reports of individuals with Noonan syndrome have revealed an association with several autoimmune diseases, including vasculitis and anterior uveitis, but no reports of systemic lupus erythematosus (SLE). Here we present the first case report of a 21‐year‐old man with a clinical diagnosis of Noonan syndrome and a recent history of mitral valve dysfunction and systemic lupus erythematosus. We discuss his findings in the context of known features of Noonan syndrome and propose that individuals with Noonan syndrome be regularly monitored for associated autoimmune phenomena. © 2001 Wiley‐Liss, Inc.