The objective of this study was to determine if a correlation exists between the effective renal plasma flow (ERPF) and the extraction fraction (EF) using 99mTc MAG3 in children. This EF has been previously described with 9mTc DTPA. However, the renal imaging agent of choice has become 9mTc MAG3.The study was approved by The Children's Hospital of Philadelphia's institutional review board. Informed consent was also obtained A retrospective study of 29 children (16 males, 13 females) of ages 1 month to 19.5 years who underwent 99mTc MAG3 renal scintigraphy from September 2001 to December 2001 was analysed. EF values were calculated with and without attenuation correction in each kidney by determining the counts in a region of interest, correcting for background and comparing the counts with the injected dose. The EF was compared to the ERPF calculated using the Schlegel's method. The correlation between the EF and the ERPF corrected and non-corrected for soft tissue attenuation, were determined and were identified by using linear regression analysis.There was significant correlation between the ERPF and the EF with (r = 0.62, p < 0.05 on the left, r = 0.51, p = 0.005 on the right) than without attenuation correction (r = 0.54, p = 0.003 on the left, r = 0.42, p = 0.022 on the right).These results indicate a correlation of the ERPF calculated using the Schlegel's method with EF obtained from a 99mTc MAG3 renal scintigraphy. The EF may be the good alternative parameter for calculation of renal function, potentially more practical in pediatric patient and the ERPF for 99mTc MAG3 using the established software program based on Schlegel's formula.