Cot death is the most important cause of death during the first year of life after the newborn period in Norway. A case control study was performed by sending questionnaires to 188 cot death parents and 475 control parents with infants matched for age, sex and time of birth. 76% of the cot death parents and 79% of the control parents completed the questionnaires. The male/female ratio of the babies in both groups was 64/36. The age distribution showed a peak between two and four months. 65% succumbed during the winter months. During the winter 32% died outdoors. This was true for only 16% of those who died during summer. A higher proportion of the cot death cases than the controls were premature (more than eight weeks). 78% of the cot death victims usually slept prone, whereas this was true for only 50% of the controls (p < 0.01). 91% of the cot death victims were found dead in a prone position. When comparing live babies during the first three months of life, significantly more cot death mothers than control mothers had stopped breastfeeding. A larger proportion of the cot death victims than the controls had had apparent life threatening events (p < 0.01). Foam mattresses were equally frequent in both groups.