In a retrospective study spanning five years, the histologic sections of 35 autopsies of infants diagnosed as SIDS victims were reviewed. Based on a recently reported study in which findings on marked basement membrane thickening (BMT) in the true vocal cords was suggested as a pathognomonic marker of SIDS, we expected to find BMT in all these cases. However, in seven of the reviewed autopsies (20%) no BMT was detected. Examination of new histologic sections of all the victims revealed myocarditis in these seven cases. In a control group (n=18) of children with known cause of death, neither BMT nor myocarditis were found. The incidence of myocardial diseases in infants and young adults (20% and 22% respectively) reported in the literature indicates that myocarditis is not a rare cause of sudden death in infants. Therefore, in SIDS-suspected cases a meticulous post-mortem microscopic examination of the heart should be carried out, especially whenever BMT of the vocal cords is absent.