Abstract Although serum creatinine has traditionally been used as the preferred marker of kidney function in the follow-up of renal transplant patients, there are several problems that make it inadvisable to use. Criterion standard measurements of glomerular filtration rate (GFR) using an exogenous agent allow a very precise estimation of kidney function; but they are cumbersome, expensive, and time consuming, and not all centers have them available. A simpler option is to estimate GFR from creatinine- or cystatin C–derived equations. These formulas have been compared in several reports in kidney transplant recipients. These reports have found discordant results about what equation is the best to use in kidney transplant recipients. Every equation performs better in the group or subgroup of patients in which it was developed or in populations with similar characteristics. In general, equations derived from the “Modification of Diet in Renal Disease” study have shown better accuracy, higher grade of correlation, and lower bias to estimate GFR in renal transplant patients than the other equations. Although cystatin C–derived equations seem to perform better than creatinine-derived equations, further studies will be necessary to know their role in the kidney transplant field.