Bone disease is an important feature of multiple myeloma, and hypercalcaemia is a frequent complication of this disease. We examined the association between serum calcium and quality of life (QOL) scores of 686 multiple myeloma patients at the time of diagnosis. Data from two Nordic studies using the EORTC QLQ-C30 questionnaire were analysed by means of linear regression analysis and a curve fitting program. Serum calcium was independently related to appetite loss, nausea/vomiting and physical functioning (P < 0.001) and to cognitive functioning (P = 0.001), i.e. scores reflecting symptoms that are well known in non-malignant hypercalcaemia. In addition, we found a highly significant independent relationship between serum calcium and the scores for fatigue and pain (P < 0.001). Serum calcium appeared to be as strong a predictor for fatigue as the concentration of haemoglobin. A cubic model (y = a + bx3) fitted the data slightly better than the simple linear model (y = a + bx) and suggested worsening QOL scores at levels of serum calcium above 2.5-3.0 mmol/L. Hypercalcaemia in patients with multiple myeloma seems to be associated with the same symptoms as in non-malignant hypercalcaemia. In addition, an increased level of serum calcium may aggravate the pain and fatigue caused by the skeletal disease itself.