We describe a 38-yr-old polio survivor with newly developed weakness from myotonic dystrophy. He suffered muscle atrophy and weakness in his legs as a result of poliomyelitis at the age of 3 yrs. After a stable interval of about 30 yrs, he felt new weakness and fatigue in his legs. Electromyography revealed generalized myotonic discharges, early recruitment, and findings of chronic denervation in his left leg. Genetic testing was consistent with myotonic dystrophy type 1. A biopsy from the right gastrocnemius revealed findings of both myotonic dystrophy and chronic denervation. This case report shows the importance of considering other uncommon conditions in the differential diagnoses of postpolio syndrome.