Diabetes mellitus is a challenging illness that has many lifestyle demands and poses life-threatening and debilitating complications. The treatments are complex and require patient education and constant vigil. Consequently, there has been increasing interest in the effects of diabetes on health-related quality of life (HRQOL). Both Type I and Type II diabetes appear to impact on HRQOL, with Type I diabetes having the greater negative effect. Of interest, the use of intensive treatment methods for Type I diabetes is not associated with decreased HRQOL. This result was reported in the Diabetes Control and Complications Trial, and so may reflect patient selection or the degree of support available in a clinical trial. However, it does suggest that intensive treatment can be undertaken without fear of inevitable decrements in patient well-being. Insulin taking type II patients experience worse HRGOL than those on oral agents or diet alone. Some new measures are now available for assessing HRQOL and related constructs in diabetic patients. In particular, the diabetes quality of life measure has been shown to be a reliable and valid indicator of HRQOL. There is a need to better understand the effects of diabetes and its treatment on HRQOL in the context of clinical practice. Such measures can facilitate this evaluation process.