Sudden infant death syndrome (SIDS) is the commonest cause of death in children over one week of age. Norway has the highest incidence in Scandinavia and the figure has increased during the last 20 years. There has been much discussion as to whether sleeping in the prone position rather than in the supine or lateral position may be a predisposing factor to cot death. In all 14 studies in seven countries where the question has been investigated, there was a higher proportion of prone infants in the SIDS group than in the control group. Intervention studies have shown that reducing the proportion of infants sleeping prone was followed by a reduction in cot deaths. There is also evidence that overheating is a risk factor for SIDS. In one British study it was found that infants who died of SIDS had more clothes on, and blankets covering them, and that both prone position and overheating were independently associated with SIDS. A possible mechanism is that overheating interferes with respiratory control. Although we do not completely understand the mechanisms underlying the links between SIDS and the prone position, the epidemiological evidence and the evidence from intervention are now so strong that it is fully justified to advice against the general use of the prone sleeping position for babies.