Reports of cerebral palsy prevalence rates per live births in recent decades in western nations show à mixed pattern. Declining rates were noted in Bristol, England, and in Denmark; but more recently à rising rate was noted in Ireland. In Western Sweden à decline has been followed by à recent rise, and in Western Australia à rise has been followed by à decline. Rates with not statistically significant changes have ben found in Iceland and Birmingham, England, and over the seven-year span of the US Collaborative Perinatal Project, although their over-all direction was downward. No single factor is likely to explain the trends observed.