Functional disability in rheumatoid arthritis (RA) reflects the cumulative effects of the disease over time and is an important outcome measure. Various factors are responsible for functional disability, such as pain, swollen joints, joint tenderness and damage, deformities but also fatigue and depression. The most commonly used instrument for evaluating functional disability in RA is the health assessment questionnaire (HAQ), a self reported questionnaire. Numerous longitudinal studies have attempted to identify predictors of disability in RA and their results show that the most common variables associated with future disability are baseline HAQ or its variation during the first year of follow-up, female sex and old age. The HAQ score is a valuable indicator of disability in RA and has been shown to be predictive of loss of employment and mortality in RA. It may therefore be regarded as a relevant outcome variable in clinical trials and for the management of patients with RA in clinical practice.