Online hemodiafiltration (OL-HDF) and medium cut-off (MCO) dialyzers augment diffusion-based hemodialysis (HD) with convective clearance to enhance removal of middle molecules. In large-scale randomized trials, OL-HDF appears to reduce all-cause, cardiovascular, and infection related mortality compared to high-flux HD, particularly when convection volumes exceed 23 L per session. Data suggests a graded effect; higher achieved convection volumes are associated with greater benefit, and advantages are observed across analysed subgroups.