The stability of the diagnosis of cerebral palsy from 2 to 5 years of age was examined in 83 children of birthweight under 1000 gm, and 112 of birthweight 1000 to 1500 gm. In 20 2-year-old children with cerebral palsy, the diagnosis persisted in 11 (55%, 95% confidence intervals 35.1 to 76.9%); 2 of 175 children (1.1%) free of cerebral palsy at 2 years of age subsequently developed the condition. Severe or moderate cerebral palsy at 2 years persisted in all eight children (100%). In 9 of 12 children in whom cerebral palsy at 2 years had disappeared by 5 years, minor neurologic abnormalities and left-hand preference occurred frequently but mean psychologic tests scores were similar to children always free of cerebral palsy. In this cohort, cerebral palsy at 2 years was not a static condition, but overestimated later prevalence.