Quality of Life (QOL) is a composite descriptor applied to an unlimited spectrum of tangible and intangible parameters of life satisfaction and capacity. Because of the breadth of determinants of QOL, most researchers prefer to focus on a specific segment of it, such as health-related quality of life (HRQOL). Generally, HRQOL indices incorporate physical, emotional and social aspects of both health perception and function. Most instruments are also subjective and quantitative. As in clinical trials, several elements are critical to the development of a HRQOL measure. Most importantly, the putative application of the instrument should be determined beforehand. The clinical setting and disease-specific population of interest must be identified. The questionnaire must be as simple as possible and easy to administer. The final instrument must be shown to be a valid measure of HRQOL, which is reproducible, with limited variability and observer bias on repeated administrations, when no clinical change has occurred. If applicable, the instrument should demonstrate responsiveness to important changes in clinical status. Finally, the value of the instrument in relevant clinical studies should be demonstrated. The critical phases of development of the McMaster IBDQ are outlined. The IBDQ is a quantitative index of HRQOL intended as a measure of therapeutic outcome for clinical trials in patients with inflammatory bowel disease.