Since a previous survey in the Valais Canton had shown a disparity in the prevalence of chronic dialysis patients compared to the national mean, an epidemiological survey was conducted in the cantons of Valais (VS) and Vaud (VD) among all the dialysis units (VS 6, VD 6) and all adult dialysis patients (VS 130, VD 187). The survey confirms the disparity in prevalence: VS 476, VD 340 and Switzerland 329 per million inhabitants (p.m.h.). This disparity also exists among different parts of the VS canton: Haut-Valais 316, Valais Central 650 and Bas-Valais 409 per million d'habitants. The mean age at start of therapy and at the time of the survey are comparable: 57 +/- 17 vs 55 +/- 15 years and 62 +/- 15 vs 61 +/- 14 respectively. Among the different etiological diseases, vascular nephropathies are less frequent and hereditary diseases more frequent in the VS canton. Co-morbidity factors were comparable. In VS there are less patients on peritoneal dialysis (6 vs 19%) and on the transplant waiting list (12 vs 16%). Globally, disparities exist in the prevalence of dialysis patients between the 2 cantons; they can be explained by both medical factors (type of nephropathies) and different options in the treatment modalities.