Acute renal failure (ARF) in children, which occurs in a variety of settings and whose differential diagnosis is best approached by age of the patient, presents a unique challenge to even the experienced pediatric nephrologist, with respect to proper diagnosis and adequate therapy. Efficient dialytic clearance, if warranted, is possible in virtually all children, using peritoneal dialysis (PD), hemodialysis (HD), continuous arteriovenous hemofiltration (CAVH), or continuous venovenous hemofiltration (CVVH), with or without dialysate. The choice of modality employed is most often guided by the child's clinical condition, and experience locally with the particular modalities. Clearly, HD, CAVH, and continuous arteriovenous hemofiltration with dialysis (CAVHD) require greater technical expertise, most often from a pediatric nephrologist. Maximum achievable clearances differ for each age-group and need to be considered when prescribing such therapies for ARF. Careful attention to the unique catabolic needs of the acutely uremic child is warranted as well. Technical advances will facilitate renal replacement therapies in the smallest of pediatric patients with ARF. It is hoped that with an enhanced understanding of the unique needs of children with ARF, both of the disease processes and their therapies, the disappointing outcome of ARF in children will be reversed.