Health-related quality of life (HRQOL) provides a multidimensional perspective that encompasses a patient's physical, emotional, and social functioning. Generally, patients with more than one co-morbid condition report the poorest level of HRQOL, but some chronic conditions, like diabetes mellitus, are strongly associated with poor HRQOL. Diabetes mellitus permanently changes a patient's life. Measures of QOL in chronically ill patients provide an important source of medical information in addition to laboratory or diagnostic tests and are becoming increasingly relevant to controlled clinical trials. Different instruments (questionnaires) have been developed to measure the psychological, physical, and social aspects of QOL for diabetes patients.