Background: Severe hyper- and hyponatraemia is associated with significant risks, yet its correction can also have serious consequences when implemented too fast or inadequately. The safe correction of serum sodium levels is particularly challenging when renal replacement therapy (RRT) is required. Methods: Using 2 case scenarios, we aim to illustrate a simple method of correcting hyper- and hyponatraemia safely by step-wise manipulation of the dialysate/replacement fluid. Results: During continuous RRT, hypernatraemia can be corrected effectively and safely by adding small pre-calculated amounts of 30% NaCl to the dialysate/replacement fluid bags aiming for a [Na+] in the fluid that allows safe equilibration and correction of the serum [Na+]. To correct hyponatraemia safely, pre-calculated amounts of sterile water can be added in a step-wise manner to achieve a fluid [Na+] that equals the desired target serum [Na+]. Conclusion: During continuous RRT, the step-wise adjustment of [Na+] of dialysate/replacement fluids offers a safe and reliable method to correct sodium disorders.