Adult-onset Pompe disease (acid maltase deficiency, glycogen storage disease type II) should be considered in the differential diagnosis in the adult patient presenting with slowly progressive selective lower extremity weakness, specifically of the hip flexors. Hip flexion weakness may be the only finding in the earliest stages of this disease. EMG findings of myotonic discharges occurring predominately in the lower extremities or paraspinal muscles, in combination with the clinical presentation, is a clue to the diagnosis of late-onset Pompe disease. Testing of all 3 paraspinal muscle levels may be useful in an otherwise normal EMG when Pompe disease is suspected.