We describe a 65-year-old female with bilateral staghorn calculi who presented with a Proteus mirabilis perinephric abscess secondary to a ruptured lower pole hydrocalyx. Radiologic evidence was consistent with underlying medullary sponge kidney (MSK) disease. Despite expectations to the contrary, MSK, a disease notable for many risk factors capable of precipitating staghorn disease, is rarely associated with coexistent staghorn calculi. A discussion of the concurrent risk factors and a possible hypothesis regarding the lack of coexistence follows.