The authors have observed a hand- and arm-squeezing behavior that seems to be highly characteristic of Smith-Magenis syndrome (SMS). This behavior serves as a useful diagnostic marker for SMS, a disorder in which the physical phenotype is often subtle. The squeezing behavior appears to be part of a complex upper-body tic which is exacerbated by happiness, excitement or overstimulation. The tic most often manifests as a 'self-hug', and is frequently associated with facial grimacing. Fleeting arm- and hand-squeezing movements may be repeated hundreds of times over the course of a day, but they do not significantly interfere with other hand functions. The excitable self-hugging in people with SMS may be one of the more benign and appealing aspects of their behavioral phenotype.