Two patients with Steinert's myotonic dystrophy are presented. The disease was suspected because of alterations in orofacial musculature clinically manifest as difficulties in swallowing, mastication, and speech, and as occlusal anomalies and maxillary bone deformities. The presumed diagnosis was reached as a result of the presence of percussion myotonia of the tongue; confirmation was based on family antecedents, electromyographic alterations, and muscle histopathologic findings.