Prader-Willi syndrome (PWS) is caused by either the structural loss of material or the absence of gene expression from the paternally inherited copy of chromosome 15 in the q11-q13 region. In addition to a well-described behavioral phenotype that includes hyperphagia, obsessive-compulsive symptoms, disruptive behavior, and an increased risk for mood disorders, recent evidence also suggests that some individuals with PWS have repetitive behavior and social deficits reminiscent of autism spectrum disorders. In particular, it appears as if those with maternal uniparental disomy (UPD) as the cause of PWS are at greater risk for autistic symptomatology than those with paternal deletions of 15q11-q13. These findings are particularly intriguing in light of data implicating maternal duplications and triplications of the same chromosomal interval in idiopathic autism, as well as evidence that functional alterations of genes in this region are associated with social deficits found in a variety of neurodevelopmental disorders. This paper will review the recent evidence for phenotypic similarities between autism and PWS and the risk of symptomatology for the UPD subtype.