The diagnosis and treatment of lateral foot pain is often difficult. The differential diagnoses are numerous, including osseous abnormalities, sprains, peripheral mononeuropathies, and radiculopathy. An often overlooked cause of lateral foot pain is sinus tarsi syndrome. From a review of the literature, it appears that even when the diagnosis of sinus tarsi syndrome is made, the biomechanics of the foot and ankle are not considered. The following is a case study of a patient with sinus tarsi syndrome treated successfully through biomechanical evaluation, and fabrication and use of custom-molded orthoses.