Two autopsied cases are presented, one involving a 5-month-old infant, and a 6-month-old infant both of whom died suddenly and unexpectedly. The incidence of sudden infant death syndrome in Japan is 1.2 per 1,000 babies live births. Among all cases autopsied in the departments of legal or forensic medicine in 78 universities or colleges of Japan, the incidence was 15 (0.5%) per 3,329 in 1984 and 20 (0.6%) per 3,150 in 1985.