Cornelia de Lange syndrome is reported to be associated with self-injurious behavior (SIB) and social avoidance. We used analog methodology to examine the effect of manipulating adult social contact on social communicative behaviors and SIB in 16 children with this syndrome. For 9 participants engagement behavior was related to levels of adult attention, and SIB showed significant variability across conditions for 3 participants. These findings indicate that SIB can be affected by environmental factors, even though it is thought to be part of the behavioral phenotype of Cornelia de Lange syndrome and suggest that individuals with this syndrome show socially motivated attention-soliciting behaviors. The implications for gene–environment interactions are discussed.