Myotonia dystrophica, described first in 1909 by Steinert, is a multisystemic disorder inherited as a dominant trait.

In addition to generalized weakness, gait disturbance and myotonia, the clinical features include prominent facial weakness, mild limb weakness, swan-line neck posture, frontal baldness, cataract, infertility, abnormal ECG finding, dysphagia, recurrent pulmonary infection, megacolon, hypersomnia, hypothyroidism, abnormal glucose and insulin metabolism, and mental defect.

We present here the clinical features, EMG, muscle biopsy, and other laboratory findings of two patients of one family who have adult onset myotonia dystrophica.