A newborn girl with extreme cardiomegaly discovered by fetal ultrasound after 34 gestational weeks is presented. The girl was delivered through a Caesarean section. After birth, multiple skeletal stigmata and generalized cardiac involvement with abnormal valves and dilated great arteries suggested Marfan syndrome. The girl died at the age of 10 h. The postmortem examinations showed cardiovascular lesions typical of Marfan syndrome. Immunofluorescence studies from cultured fibroblasts of the patient showed decreased amounts of immunostained fibrous material, supporting the clinical diagnosis of a severe Marfan syndrome.