Renal failure, proteinuria and proximal tubular acidosis are the features of cidofovir renal toxicity, its main side-effect. Proteinuria occurs in more than 40 per cent of patients and correlates with early renal dysfunction. A fall in serum potassium, bicarbonate, uric acid, calcium and phosphorus levels associated with glucosuria is the hallmark of proximal tubular acidosis. Most of the patients exhibit only glucosuria. Renal failure, diagnosed in 12 per cent of treated patients, is a late feature, usually discovered after the onset of proteinuria and glucosuria. Prevention of cidofovir-induced renal toxicity involves a search for other risk factors, probenecid treatment, and requires an optimal hydration status.