Rabbits and guinea pigs are often diagnosed with urolithiasis, and additionally, rabbits often have sludgy urine (thick, calcium carbonate sediment in the bladder). Urolithiasis is a frustrating disease for veterinarians and owners due to the common recurrence of calculi, especially in guinea pigs, with an estimated recurrence rate of 13.9-60%. Additionally, sludgy urine can lead to signs of lower urinary tract disease and present with a variety of clinical signs such as inappropriate urination, stranguira, pollakiuria, and "tooth-paste" urine. While dietary calcium limitation in rabbits is critical in preventing these problems, additional medical management may reduce the risk of recurrence. This lecture discusses the authors' recommended medical management for these diseases in rabbits and guinea pigs. Hydrochlorothiazide, a thiazide diuretic, is often dosed by the authors at 1 mg/kg q12 h. Hydrochlorothiazide is a calcium-sparing and potassium-losing diuretic that helps to improve diuresis, thus reducing hypercalciuria. In dogs and cats, potassium citrate is given as a urinary alkalinizer. However, citrate does not alkalinize the already alkaline urine (pH of 7-8) of rabbits and guinea pigs. Potassium citrate increases citrate levels in the urine, which complexes with calcium ions into a water-soluble salt. Citrate also inhibits the spontaneous nucleation of calcium phosphate. It is typically dosed at 40-80 mg/kg q12 h. In the authors' experience, both medications have no overt adverse effects, and clinical hypokalemia has not occurred. However, the authors recommend repeating a complete blood count, chemistry panel, and urinalysis every 3-6 months to monitor the patient.