Fatigue has been widely assumed to increase after major surgery, and possible physical explanations have been intensively investigated. Nevertheless, existing data are almost exclusively from abdominal surgery and are based on the use of a single visual analogue scale. Moreover, no physical basis has been found. The present study used a more homogeneous surgical model than has been employed hitherto in order to find whether fatigue was related to emotional state. We measured fatigue before and 1 and 7 weeks after major joint arthroplasty in 63 patients, using a questionnaire that separates mental and physical fatigue. Physical function and subjective emotional and somatic state were measured at the same times; optimism was measured preoperatively. Neither mental nor physical fatigue increased after this form of surgery. Mental and physical fatigue each correlated with low positive mood throughout. The best predictor of physical fatigue postoperatively and at follow-up was preoperative physical fatigue. Preoperative mental fatigue and negative mood were independent predictors of mental fatigue postoperatively and at follow-up. Preoperative fatigue also predicted worse subjective emotional and physical state after surgery. These results suggest that fatigue should be regarded as an aspect of emotional distress perioperatively and that complaints of fatigue postoperatively may reflect the tendency to complain of fatigue or negative mood preoperatively rather than being attributable to surgical trauma.