Data were analyzed from all cases of cerebral palsy in a population-based register in Western Australia. The number of cases of cerebral palsy diagnosed by age 5 years varied little among cohorts of infants born between 1960 and 1982. Trends toward more intensive perinatal care, increasing frequency of cesarean section, and the increased use of electronic fetal monitoring to detect fetal distress were associated with decreases in perinatal mortality but not in cerebral palsy. The increase in survival of low birth weight infants has resulted in an increased number of children with cerebral palsy, but this has had a minimal impact on total cerebral palsy rates. These descriptive trends raise doubts about the relationship between cerebral palsy and perinatal events, the effects of obstetric and neonatal interventions in reducing cerebral palsy, and the use of cerebral palsy data as an index of perinatal care practices.