Single photon emission computerized tomography (SPECT) scintigraphy has proved to be an extremely sensitive renal imaging modality in children with genitourinary pathology, including pyelonephritis, particularly when compared to 2-dimensional planar imaging. This study was undertaken to corroborate SPECT dimercaptosuccinic acid (DMSA) scintigraphic findings with specific histopathology in acute pyelonephritis. Unilateral vesicoureteral reflux was produced in 19 Yorkshire piglets 3 to 4 weeks old. The bladders of 12 animals were inoculated with Escherichia coli 2 weeks later, after baseline SPECT DMSA scans had been obtained. The animals were then re-imaged at 3 (4), 7 (4) or 14 (4) days after infection and sacrificed for histological evaluation. Seven purposefully uninfected piglets with unilateral reflux served as controls and were followed for up to 6 weeks before imaging and sacrifice. SPECT proved to be 97% sensitive and 93% specific in providing the diagnosis of acute pyelonephritis. The SPECT findings were manifest by a spectrum of abnormal findings (mottling, striations, inner cortical scalloping and focal cortical defects), which correlated precisely with the extent and severity of cortical involvement in the acute pyelonephritic process. We propose a new classification scheme for SPECT DMSA renal scintigraphic imaging, and believe that this modality is exquisitely sensitive in providing the diagnosis as well as in evaluating the extent of renal parenchymal involvement when acute pyelonephritis is induced in the animal model.