The recent issue of Pediatrics reports on a study of 235 infants with plagiocephaly ("flat head" syndrome). The researchers found a relationship between plagiocephaly and developmental delay. Infants with plagiocephaly were twice as likely to exhibit developmental delays compared to the control group. They could not determine if one causes the other though. The investigators stressed that babies should still be put on their backs to sleep.
Reference: Speltz M, et al "Case-control study of neurodevelopment in deformational plagiocephaly" Pediatrics 2010; DOI: 10.1542/peds.2009-0052.