Introduction; Congenital myotonic dysrtrophy (DM) is an inherited autosomal-dominant multisystemic disease, exclusively maternal transmission. The DM is associated with the unstable expansion of CTG trinucleotide repeat on chromosome 19q13.3. We report a congenital DM infant who presented chylothorax and hypertrophic cardiomyopathy in the first year. Case; A 38 year-old nullipara was transferred because of fetal hydrops, and polyhydroamnios at 28 weeks and 4 days of gestation. She had three times of amnioreduction from 29 to 32 weeks of gestation. The preterm labor pain and fetal distress developed at 34 weeks and 5 days of gestation, the emergent Caesarian section was performed. After birth, he presented little respiratory effort, and he was intubated immediately, then positive-pressure ventilation was started in the delivery room. He had characteristic features; inverted v-shapped upper lip, low set-ears, bilateral equinovarus talipes deformity, clenched fist, bilateral cryptochism, and macrocephaly. The respiratory distress developed on day 11, the chest X-ray revealed bilateral pleural effusion. The white pleural effusion was compatible with chylothorax; white blood cell count of 2,850/μL with 97% lymphotcytes, triglyceride 1,320mg/dL, and protein 3.1g/dL. It resolved with chest-tube drainage, and feeding of medium-chain triglyceride enriched formula without any medical or surgical treatment. He failed to wean the mechanical ventilation several times due to weak spontaneous respiratory effort. The tracheostomy was done at 4-month of age. We performed echocardiogram monthly, the hypertrophic change of interventricular septum (IVS=7.88 mm, z-score 5.69) and posterior wall of left ventricle (LVPW=7.30 mm, z-score 4.92) at 6-month-old was checked. He was discharged with home ventilator, continuing rehabilitation treatment, and medication of beta-blocker on day 240. His mother and he were diagnosed with DM by PCR-Southern DNA analyses using their peripheral lymphocytes. Conclusion; In case of accompanying with pleural effusion in congenital DM, it needs to consider chylothorax, and identify whether DM is related to thoracic duct defects. Although cardiac manifestation is rare in congenital DM, it needs regular screening of echocardiogram to detect early change of cardiac structure and start preventive intervention before deteriorate condition.