Three patients with aberrant muscles passing through Guyon's canal are described. Each of the three patients experienced, among other symptoms, dysesthesias on the volar aspects of the little and ring fingers. The anomalous muscle in two of these patients arose from the antebrachial fascia just proximal to Guyon's canal, traveled through the canal, and inserted with the abductor digiti minimi muscle. This anomaly was bilateral in both patients. In the third patient the abductor digiti minimi muscle originated radially from the transverse carpal ligament, and this variant too was bilateral. Symptoms in each of the 3 patients resolved following surgery. Ulnar nerve compression at Guyon's canal is discussed and the literature is reviewed. Although anomalous muscles occur frequently in this location, the anatomic variant found in patient 3 has not yet been described in the literature.