Although the supine sleep position in infants has greatly reduced SIDS incidence, it has been associated with an increase in referrals of positional, or non-synostotic, plagiocephaly (NSP). Deformation of the soft infant skull may occur in response to the exertion of gravity on the cranium lying on a firm surface, particularly in the presence of a favoured head position. NSP is characterised by patent cranial sutures and unilateral or central occipital flattening, often with associated compensational changes in other parts of the cranium. Differentiation between lambdoid synostosis and NSP can largely be made using clinical examination. The condition is common and most mild to moderate cases of NSP revert to the normal range by the age of two years. At increased risk are males, firstborns, non-singletons, premature infants, less active infants, those exposed to intrauterine crowding or a difficult delivery, supine sleepers and infants with neck rotation abnormalities. It is unclear at present whether developmental delays that are sometimes associated with NSP are causal or resultant of plagiocephaly. Treatment involves keeping pressure off the flattened part of the skull and treating neck rotation abnormalities. Prevention revolves around early awareness of the head shape and varying the head-lying position from birth.