Estimating glomerular filtration rate (GFR) is important for clinical management and research studies in simultaneous pancreas-kidney transplantation (SPK) recipients. No study has specifically investigated the reliability of recent creatinine-based GFR estimating equations in this singular population. We assessed the performances of CKD-EPI, MDRD, Schwartz-2009, Schwartz-Lyon, Lund-Malmo and Full Age Spectrum equations for estimating GFR after SPK. 126 patients were included. GFR was measured by a reference method (mGFR) one year after SPK and estimated with the different equations from a standardized measure of serum creatinine. Relative bias, precisions, 10% and 30% accuracies (P30) were used to determine equations reliability. Ages ranged from 29 to 58. Mean mGFR was 56.3 \textpm 13.3 [23.6-92.5] ml/min/1.73 m2 . In the whole population, P30 of the CKD-EPI and MDRD equations were 42% (38.0; 46.0) and 65% (61.5; 69) respectively. As compared to the other equations, the Schwartz-Lyon equation was significantly more accurate (P30 = 86.0% [83.5-88.0], P \textless 0.01) and less biased (1.13 [1.06-1.19], P \textless 0.01). Conclusions were similar whatever the age class (\textless40 or >=40) and mGFR level (\textless60 or >=60 ml/min/1.73 m2 ). This study suggests that the CKD-EPI and MDRD equations have poor performances in SPK recipients and that the Schwartz-Lyon equation is a reliable alternative.