Sudden Infant Death Syndrome (SIDS) is the term first proposed in 1969 for a distinctive subgroup of unexpected infant deaths occurring during the first months of life, with relatively consistent clinical, epidemiological and pathological features, which remain unexplained after a thorough case investigation, including a complete autopsy, examination of death scene and review of clinical history. Sudden infant death unnecessary means SIDS. According to definition, SIDS remains a diagnosis of exclusion, distinguished from others only by subjective and permissive variables. Despite the vague and permissive nature of the definition, epidemiological studies identified some risk factors as prematurity and social disadvantage. Nevertheless, the most interesting findings are those related to environmental and care features, as drug addiction and/or smoke exposition during pregnancy, sleep position of the infant, environmental temperature, parental bed sharing and breast feeding. Those factors play a variable role, but their correction reduced SIDS incidence. Sudden infant death is a diagnosis made by expert pathologists with pediatrician's and investigator's advice, based primarily on autopsy findings and death scene investigation performed through the severe application of investigative protocols.