A 14-year-old Arabian gelding presented to the Cornell University Equine and Farm Animal Hospital Large Animal Medicine Service in August 2003 with a chief complaint of weight loss, polydipsia, polyuria, and dysuria. Upon rectal palpation, a large cystic calculus and bilaterally enlarged ureters were noted. The chemistry panel was consistent with renal failure and urinalysis showed isosthenuria. Further diagnostics included ultrasound of the kidneys, and endoscopy of the urinary bladder. During rectal examinations, the urolith was noted to rest at the trigone region, thereby possibly obstructing the ureters. The horse was stabilized on fluid therapy and a cystotomy was performed to remove the urolith. Post-operatively, renal function was markedly improved, but the horse was ultimately euthanized due to Salmonellosis. Postmortem findings included severe hydronephrosis, hydroureter, and chronic severe cystitis. This case report illustrates the unusual relationship between chronic renal failure and cystic calculi in this horse.