To investigate the sudden death of a 31-year-old man, a medicolegal autopsy was performed. Major findings were a dilated aortic root with a longitudinal rupture of the intima and dissection of aorta and right coronary artery and consequent tamponade of the pericardial sac. Moreover, arachnodactyly and other skeletal deformities in combination with the histological finding of a pseudocystic medionecrosis of the aortic wall were noted. By sequencing of the FBN1 gene, a mutation (1622G>A) leading to the diagnosis of Marfan syndrome was found. Genetic counseling was recommended to the relatives who reported that the father of the deceased had died at the same age from aortic rupture. While fortunately the child of the deceased lacked this mutation, it was found in his younger sister. The results of the autopsy thus enabled early diagnosis and beginning of treatment in the sister and thus a considerable statistical increase in lifespan. With this report, we want to show that medicolegal autopsies can also have medical consequences for relatives. We argue that in all sudden and unexpected deaths in young persons up to 35 years an autopsy should be performed, not only to detect unnatural causes of death but also to identify heritable diseases and thus aid the relatives.