Our research on SIDS two decades ago led to prevention campaigns, which substantially reduced mortality. However, currently mortality in New Zealand is higher than that in comparable countries and is especially high in Maori. Seventy infants a year die suddenly and unexpectedly, and 45 are Maori. Over 50% die while bed sharing. Advising parents not to bed share with baby has met with opposition and has not resulted in behavioural change. We propose a nationwide case-control study of all sudden unexpected deaths in infancy (SUDI) over a three-year period. We expect there will be 210 SUDI cases and these will be compared with 420 control infants and their families. The aim of the study is to identify the risk factors for SUDI, especially in Maori. It will specifically look at modifiable risk factors, particularly those relating to bed sharing and what makes bed sharing safer or more dangerous.