The objectives of this retrospective study were to assess the clinical applications of mandibular step osteotomy (MSO) and to evaluate its long-term clinical morbidities. A total of 152 patients with MSO performed between 1990 and 1999 were assessed. Forty-two patients were successfully recalled through questionnaires and clinical parameters for clinical evaluation, which included (1) tooth sensibility; (2) periodontal status; (3) neurosensory deficit in terms of light-touch threshold, 2-point discrimination, and pain threshold; and (4) temporomandibular joint function. The patients were finally asked about their overall satisfaction with the surgical treatment. The result revealed that MSO was commonly indicated for the correction of mandibular hyperplasia. Clinical assessments showed that 2.75% of the teeth assessed had negative pulpal response, 3.9% showed mildly increased probing depth, and another 3.9% showed gingival recession. Neurosensory assessment revealed that 31% of the operating sites had an increased light-touch threshold, 4.8% had heightened 2-point discrimination, and 9% had an elevated pain threshold. Also, 9.7% of the patients showed reduced mouth opening and 17% had mild tenderness of masticatory muscles. Of all the patients assessed, 12% were not satisfied with the orthognathic treatment. The reasons included relapse, residual asymmetry, and persistent paresthesia.