Objective: To describe the potential benefits of simultaneous anterior-posterior dynamic renal scintigraphy (DRS) in congenital abnormal kidneys (CAK). Material and Methods: Simultaneous anterior-posterior projection DRS with 99mTc diethylene triamine pentaacetic acid (DTPA) by a dual-headed gamma camera was performed in 13 CAK patients, Dynamic renal functions were evaluated visually; anterior-posterior renograms were obtained. Differential renal functions (DRF) were calculated in 7 patients using geometric means. Eight patients had dimercaptosuccinic acid (DMSA) cortical renal scintigraphy (CRS). Hypoactive areas on CRS were counted and compared with DRS on the basis whether they displayed "fill-in" with 99mTc DTPA. DRFs of DRS and CRS were compared. Results: CAK types were pelvic-horseshoe-fused triple-cross ectopic kidneys. The best visual dynamic renal function evaluation in the anteriorly located kidneys/kidney parts were obtained front the anterior images. Renograms of all the anteriorly located CAK obtained from the anterior acquisition displayed renal functions better than the posterior renograms. Twenty two out of 27 regions showing decreased DMSA uptake from the anterior projection showed "fill-in" with 99mTc DTPA on anterior views of the DRS. Sixteen of 20 posterior hypoactive regions displayed "fill-in" on posterior projection DRS images. Five regions with decreased DMSA uptake from the anterior projection and four from the posterior did not show "fill-in" pattern oil either projection in DRS. DRF of DRS were in concordance with the DRF of CRS. Conclusions: Simultaneous anterior-posterior projection DRS in CAK can assess dynamic functions of the anteriorly/posteriorly located kidneys of a patient in a single scintigraphic study, gives the oppurtunity of calculating DRF with geometric mean counts, and helps to differentiate parenchymal damage from dilated collecting systems.