Barth syndrome (BS) is a rare X-linked recessive metabolic disorder characterized by cardiomyopathy, hypotonia, neutropenia, growth retardation and 3-methylglutaconic aciduria type II. Cystic fibrosis is a common autosomal recessive genetic disorder in Caucasians. Herein, we reported a rare clinical association in an infant diagnosed based on clinical and genetic analysis. A six-month old boy admitted with chronic steatorrhea. The diagnosis of cystic fibrosis was made after clinical and laboratory examinations. Fifteen days later, the patient was presented with restlessness and moaning. He had hypoglycemia and lactic acidosis. The patient died three hours after the admission. Pedigree analysis revealed similar sudden infant deaths in close relatives. Postmortem genetic analysis revealed the diagnosis of Barth syndrome. This is the first case of the association of Barth syndrome with cystic fibrosis. Our case reinforces the importance of pedigree analysis and postmortem examinations.