To prevent early sudden infant death syndrome, the health authorities recommend that newborn infants sleep on their back. This has led to an increase of positional plagiocephaly. The aim of this study was to describe this condition and to recommend a preventive treatment.This is a retrospective registration of 133 children with positional plagiocephaly seen in the period from 1994 to 2000.The number of children with positional plagiocephaly increased from two in 1994 to a maximum of 43 in 1999. 83 were males and 50 were females. 84 were dextral and 49 were sinistral. In seven (14%) of the sinistral and three (4%) of the dextral, we found a physical explanation of the head turning. In 51 children, X-rays of the skull were performed, but no synostosis was found.The back-sleeping position of infants is a promotive factor to positional plagiocephaly which may be prevented by simple alternating head positioning. Otherwise early (< 6 months of age) corrective physiotherapy and positioning or an orthoplastic helmet must be considered. The diagnosis of positional plagiocephaly is based on clinical observations. There is a favourite head turning, an ipsilateral occipital flattening, an ipsilateral frontal bossing, and the ipsilateral ear is moved forward.