Tandem mass screening has recently been started in Japan, but genetic screening has yet to be widely performed in neonates and many unexpected deaths are still being reported. We previously reported two cases of sudden infant death that may have been prevented had newborn screening been performed. In this study, we retrospectively reviewed 71 cases of sudden infant death for 66 arrhythmia- and 63 metabolic disease-related genes to identify how many cases of sudden infant death may have been prevented had mass screening been performed. Next-generation sequencing revealed that six cases had arrhythmia-related gene variants and five cases had metabolic disease-related gene variants. Had genetic screening been performed in addition to biochemical and physiological screening during the neonatal period to identify those at risk of arrhythmia or metabolic disease, these infants could have been diagnosed and treated, preventing their deaths. As such, screening of newborns may prevent sudden infant death.