Twelve patients with chronic renal failure, on maintenance hemodialysis have a stereotyped illness. The dialysate was made up from a high level aluminium tap water. After having been on haemodialysis for 10 to 12 months, they suffer from more and more acute osteodystrophic, osteomalacic symptoms. Then, distinctive EEG abnormalities appear. These first symptoms allow an early diagnosis of the progressive dialytic encephalopathy. The neurological symptoms appear some months later. Eight patients died from this encephalopathy. Four patients are still alive and are, from at least two years, on maintenance haemodialysis with a free aluminium water. In these 4 cases, the evolution of the disease is good: osteomalacic symptoms disappear in a year; the neurological symptoms are still present though transient. EEG abnormalities remain and blood aluminium level is about 100 micrograms/L. These cases show, once more, the significant role of aluminium as an aetiological factor in "progressive dialysis encephalopathy".