OBJECTIVE:Quality of Life (QOL) is a ubiquitous yet rarely precisely defined term. QOL may be determined by the differences (gaps) between our current situation and our expectations. Contemporary methods of measuring QOL often do not take these gaps into consideration. We performed this study to develop items and methods for measuring and valuing these gaps in order to better determine individual QOL for children with rheumatic diseases. METHODS:We generated items from literature review, other QOL measures and interviews with pediatric rheumatology patients and their families. Gap-scales to measure the discrepancy between a child's current state and the expected or desired state were designed and tested iteratively in pilot interviews. RESULTS:Thirty-one children (mean age=13.5 years, age range=6-17 years) and 22 parents were recruited through pediatric rheumatology clinics. The process of item generation, reduction and preliminary formatting yielded a list of 72 items. We developed a 3-point categorical scale of importance and a vertical visual analog scale (VAS) to determine individual valuation of items. 5 gap-scales were developed to reflect different aspects of the discrepancy between the child's current and expected or desired states for different QOL items. CONCLUSIONS:We have developed a QOL interview based on theory that we can now test to see if it will enrich our understanding of the determinants of QOL in pediatric rheumatology patients and other chronically ill children.