Since the definition of supraclavicular nerve entrapment syndrome by Gelberman et al. (Gelberman et al. [1975] J. Bone Joint Surg. Am. 57:119) a number of clinical cases of this specific entrapment neuropathy have been reported. In all these cases, the nerve injury has been attributed to the location of the supraclavicular nerve branch in a narrow canal in the clavicle. However, in the anatomical literature, variations in the course of the supraclavicular nerves have not only been ascribed to bony canals but also to abnormal fibrous and muscular structures. Considering the fact that the existence of a narrow site with rigid walls along the course of a nerve is essential for the development of an entrapment neuropathy, our study examines all the variant anatomical structures with a possible role in supraclavicular nerve entrapment. We describe three groups of anatomical structures with close relation to the course of the supraclavicular nerves-transclavicular canals, fibrous bands, and unusual muscular structures. Based on the characteristics of the variations found, for the first time, we suggest that in addition to the bony canals through the clavicle certain fibrous and muscular structures could also be an anatomical basis for supraclavicular nerve entrapment syndrome.