This study evaluates stability of chronic condition identification in children older than 4 years in a health plan billing data using Clinical Risk Groups. A total of 31,055 children were continuously enrolled for 4 years; 7.5% (2,334) identified with a chronic condition status in year 1, 2002, and another 15.4% (4,784) during subsequent years; 63.6% (19,759) were identified as "healthy" throughout. The most stable were those identified with a catastrophic health condition. The least stable were those with minor and moderate/dominant major chronic conditions. Overall, 73.1% (1,706) of the children with chronic conditions in year 1 improved in status, and 5.7% (133) progressed to more complex conditions.