PURPOSE OF REVIEW: To highlight selected adverse effects of continuous renal replacement therapy and to suggest measures for reducing harm. RECENT FINDINGS: Adverse effects of continuous renal replacement therapy are related to bioincompatibility, bleeding, metabolic consequences, loss of heat, vascular access and human error. Bioincompatibility initiates coagulation and inflammation. Use of membranes with high pore size permits direct removal of the locally formed inflammatory mediators. Regional anticoagulation with citrate reduces the risk of bleeding and abolishes polymorphonuclear and platelet degranulation in the filter. Continuous renal replacement therapy is associated with increased losses of amino acids and the water-soluble vitamins carnitine and selenium. Compared to bicarbonate, lactate-buffered fluids may increase energy needs and glucose intolerance. Patients on continuous renal replacement therapy may lose heat. SUMMARY: Several measures can be considered to improve safety of continuous renal replacement therapy. Among these are the use of membranes with high pore size, implementation of citrate to reduce bleeding and bioincompatibility, supplementation of water-soluble vitamins and selenium to increase antioxidant defense, use of bicarbonate-buffered solutions in the most critically ill, and prevention of loss of heat. Last but not least, improvement of safety needs continuous training of staff for better understanding of the method.