The aim of this study was to evaluate the quality of life in patients on chronic dialysis and to research the influence of various factors related to treatment and ESRD on quality of life. The cross-sectional study was carried out nationally and 1013 randomly selected stable patients on dialysis were evaluated. The evaluation of quality of life was by the Karnofsky Scale (KS) and the Sickness Impact Profile (SIP). Both questionnaires were self-reported. Co-morbidity was evaluated according to the Friedman Comorbidity Index. Adjusted quality of life scores for case-mix differences of several groups of patients were compared. Twenty-six per cent of the patients showed severe quality of life restriction on the Global Score of SIP (score > or = 20) and 31% on the KS (score < or = 60). The partial categories of the SIP that were more affected were work, recreation and pastimes, home management, and sleep and rest. No significant differences were found relating to dialysis technique, dialysis solution, or dialyser membrane. Greater haemoglobin concentrations were related to better quality of life scores on Physical Dimension and Global Score of SIP. Advanced age and Comorbidity Index were related to worse quality of life scores. We conclude that 25% of the patients showed an important effect of the disease on their quality of life. An increase in haemoglobin was related to better quality of life in dialysis patients. Advanced age and co-morbidity both adversely affected quality of life.