Objective To summarize the clinical, neuroelectrophysiological, and genetic characteristics in patients with myotonic dystrophy type 1 (MD1). Methods The clinical symptoms and the results of electromyographic, myopathological, and genetic tests were collected from three patients with MD1. Results All the three patients (1 male) experienced an onset at adult age with a chronic disease course and presented with myotonia and muscle weakness in distal limbs; two patients had extraocular muscle or facial muscle weakness; one patient had concomitant forehead alopecia; two patients had cardiac conduction disorders such as paroxysmal ventricular tachycardia, left anterior bundle branch block, and right bundle branch block; two patients had white matter lesions. The number of CTG repeats in the 3'-untranslated region of the DMPK gene were 104, 150, and 299, respectively, in the three patients with MD1, all of which were bigger than 50. The electromyographic tests of all the three patients showed tonic discharges of muscles. Conclusions Patients with MD1 show muscle weakness mainly in distal muscle groups with cardiac conduction disorders and white matter lesions as their prominent manifestations of multiple system involvement. Electromyography can detect tonic discharges of muscles in clinical practice, which makes it the most sensitive screening method for the disease.