Pallister–Killian syndrome is a rare, multi-system developmental diagnosis typically caused by tetrasomy of chromosome 12p that exhibits tissue-limited mosaicism. The spectrum of clinical manifestations in Pallister–Killian syndrome is wide and includes craniofacial anomalies, clefts, ophthalmologic, audiologic, cardiac, musculoskeletal, diaphragmatic, gastrointestinal, genitourinary, and cutaneous anomalies in association with intellectual disability and seizures. Growth parameters are often normal to elevated at birth with deceleration of growth postnatally. No formal estimate of the prevalence of Pallister–Killian syndrome has been made. Here, we report the clinical findings in 59 individuals with Pallister–Killian syndrome who were ascertained at Pallister–Killian syndrome Foundation family meetings held in the summers of 2006, 2008, 2009, and 2010. In addition, the clinical findings of 152 cases reported in the medical literature were reviewed and compared to the cohort examined here. Several novel clinical characteristics were identified through detailed dysmorphology examinations of this cohort and reassertion of a mild developmental variant is described. This report expands the clinical manifestations of Pallister–Killian syndrome and highlights the variable expressivity of this diagnosis with important implications for diagnosis and counseling. © 2012 Wiley Periodicals, Inc.