Shroff R, et al. - Researchers propose the haemodiafiltration, heart and height (3H) study design and baseline characteristics of the study population. The 3H study represents a multi-centre, non-randomised parallel-arm intervention study within the International Paediatric Haemodialysis Network Registry to test the hypothesis that children on haemodiafiltration (HDF) vs those on conventional haemodialysis (HD) have an improved cardiovascular risk profile and growth and nutritional status. For this study, children were recruited from 28 paediatric dialysis units across Europe and in Toronto, Canada. Subjects included were 5–20 years aged undergoing post-dilution HDF or HD (incident and prevalent patients), HD or HDF for 4 h per session 3 times per week, or a single pool Kt/V > 1.2 in prevalent patients in the month preceding recruitment. Excluded subjects were those in whom a living donor kidney transplant is planned within 6 months, who had pre-dilution HDF, or had HD or HDF of any duration other than 4 h per session 3 times per week. This is the largest prospective study in children on dialysis to date.