Glomerular filtration rate is the best determinant of kidney function in children. A decline in glomerular filtration rate may be the only sign of renal disease. A knowledge of glomerular filtration rate allows the clinician to appropriately dose medications, administer fluids, and intervene early to prevent end-stage renal failure. The aim of this review is to discuss the current options for determining glomerular filtration rate in children and the latest advances in research on this topic.Owing to the limited availability of inulin, the gold standard for measuring glomerular filtration rate, and the concern for using radioactivity, the plasma disappearance of iohexol has been utilized to measure glomerular filtration rate in children, and this represents a practical option for glomerular filtration rate determination in both clinical and research studies. By contrast, creatinine-based estimates of glomerular filtration rate (e.g. Schwartz formula) are more practical for bedside use. To improve their precision, recent formulas have incorporated the use of additional endogenous markers, such as cystatin C, albumin, and blood urea nitrogen.Iohexol plasma clearances should be used to accurately measure glomerular filtration rate in children. New estimating equations with multiple endogenous markers are being developed for everyday clinical use. However, at present, there is no substitute for an accurate glomerular filtration rate determination, particularly in children with conditions affecting muscle mass or body habitus.