This chapter is concerned with sudden death in infancy, childhood and adult life. Most of the evidence for a causal role for infection in sudden death comes from studies of sudden unexpected death in infancy (SUDI) and therefore the section on SUDI and closely related conditions forms the largest part of the material presented. There is a convincing body of evidence that infection has a role in at least some cases of sudden infant death. More specifically, there is evidence, based on sound theoretical principles and supported by laboratory experiments, that some cases of sudden death can be caused by common bacterial toxins absorbed from mucosal surfaces or delivered as part of a transient bacteraemia. This idea, termed the common bacterial toxin hypothesis, is not proven beyond doubt, it remains an hypothesis, but it does offer a plausible explanation for many of the features associated with sudden death at all ages. One reason for concentrating on this idea is that we are now in a position to prove or disprove the hypothesis using the techniques of genomics and proteomics. But we will only succeed if those who perform necropsy examinations in cases of sudden death are fully conversant with the theoretical background and are ready to obtain the appropriate specimens. Large-scale studies of the mucosal microbial flora with proteomic analysis of the bacterial secretome and parallel proteomic analysis of fluids obtained at autopsy are required. This is big science requiring experts in many disciplines. The potential rewards from these studies in terms of understanding disease are considerable and it will put autopsy pathology back in its rightful place at the centre of clinical academic medicine.