The 18q- syndrome is relatively common among cytogenetic abnormalities occurring in approximately 1 in 40,000 live births. However, interstitial deletions involving 18q12.2 to q21.1 are much less common. Only 15 cases have been reported in the literature. A phenotypic pattern is emerging of mild dysmorphic features, mental retardation, behavior abnormalities, and the lack of serious malformations. We present a 67-year-old woman with minor dysmorphic features, moderate mental retardation, hyperphagia, and del(18)(q12.2q21.1). This patient is presented for the natural history of this deletion syndrome as well as the behavioral phenotype. Copyright 2003 Wiley-Liss, Inc.