A 2-year-old, spayed female Papillon, presented on July 11, 2007 for a 5-month history of stranguria, pollakiuria, crystalluria, and a history of ureteral perforation during cystoscopy for calcium oxalate urolith removal by the rDVM in February 2007. Physical examination and initial laboratory diagnostics were normal. An abdominal ultrasound depicted severe left hydronephrosis and hydroureter attributable to ureteral obstruction near the trigone of the bladder. Nuclear medicine techniques further assessed renal function using renal scintigraphy and plasma clearance (99m Tc-DTPA) analysis. The global glomerular filtration rate (GFR) was below the reference range with mild right and moderate left renal insufficiency. Ureteroneocystotomy was performed to preserve the left kidney and prevent further damage. Ureteral obstruction can be detrimental to renal function, and while there are several examinations for assessing the kidney, renal scintigraphy provides both a differential and global analysis of GFR. The GFR results for this dog helped determine the appropriate course of action: surgical relocation of the left ureter for preservation of left renal function. Calcium oxalate urolithiasis remains a problem with this patient, and long-term medical management is important for prevention of urolith formation.