To assess cross-cultural adaptation, and to validate the parent's version of a health-related quality-of-life instrument, the Childhood Health Assessment Questionnaire (CHAQ) was investigated after its translation into Japanese. A total of 132 subjects were enrolled: 63 patients with juvenile idiopathic arthritis (JIA) (34 systemic and 29 polyarticular) and 69 healthy children. The CHAQ distinguished clinically between healthy subjects and the two JIA subtypes of patients. The average disability index (DI) scores for systemic JIA (sJIA) and polyarticular JIA (pJIA) patients and healthy subjects were 1.5, 1.2, and 0.0, respectively. All variables in the questionnaire were shown to be significant (P < 0.001). Patients with pJIA showed better correlation than those with sJIA. Significant correlation was seen in the polyarticular group with CRP, ESR, parents' VAS, the number of joints with pain, and the number of active joints. However, there was even a negative correlation between DI and parent's assessment of overall well-being for the sJIA group. The Japanese version of the CHAQ was a reliable and valid tool for the functional assessment of children with pJIA. Functional ability, as assessed by the CHAQ, may not be the main consideration of sJIA patients' parents when assessing their child's status.