Although the physical characteristics of Cohen syndrome have been studied in considerable detail, data on other aspects of development are relatively limited. We report findings on cognitive, linguistic, and adaptive profiles in a group of 45 individuals clinically diagnosed with Cohen syndrome when aged between 4 and 49 years. The profile of skills observed was consistent with other recent findings. Thus, independence levels generally were poor, but socialization skills as assessed by the Vineland were relatively less impaired. This particular area of strength probably underlies the ‘sociable’ temperament typically associated with Cohen syndrome. However, the range of cognitive ability was wider than reported in most previous research, raising the issue of whether mental retardation should be considered as a necessary component of the phenotype. The implications for genetic testing are discussed.