Although it is well documented that obesity is strongly associated with morbidity and mortality, less is known about the impact of obesity on functional status and health-related quality of life (HRQL). However, in recent years research has been conducted to estimate the impact of obesity on HRQL, and to determine the effects of weight reduction on HRQL. The majority of published studies indicate that obesity impairs HRQL, and that higher degrees of obesity are associated with greater impairment. Obesity-associated decrements on HRQL tend to be most pronounced on physical domains of functioning. Studies of the effect of obesity surgery among morbidly obese patients indicate that this procedure produces significant and sustained improvements in the majority of HRQL indices; among mild-to-moderately obese persons, modest weight reduction derived from lifestyle modification also appears to improve HRQL, at least in the short term. Additional research is needed to (1) further characterize the effect that obesity has on HRQL; (2) estimate the short- and long-term effects of various methods of weight reduction (e.g. surgery, lifestyle modification) on HRQL; (3) improve both the conceptualization and measurement of HRQL to incorporate the personal preferences and values of the patient; and (4) develop ways to enhance and sustain positive changes in HRQL, even if weight maintenance is elusive. © 2001 The International Association for the Study of Obesity.