Large kidney on one side and small kidney on the other side may be caused by renal atrophy, hydronephrosis, renal tumor and so on. 1. Renal atrophy: When renal atrophy occurs in patients, the volume of the kidney on the atrophic side will be smaller than that on the normal side, which can be caused by renal tuberculosis, nephritis, vascular embolism and so on. 2. Hydronephrosis: the volume of kidney on the hydronephrosis side will be larger than that on the normal side. The causes of hydronephrosis may include stenosis of pelvic ureteral junction, neurogenic bladder dysfunction, etc. The patients will have abdominal mass and lumbar distension. 3. Renal tumor: If the patient suffers from renal tumor, the volume of kidney on the tumor side is larger compared with that on the normal side, and accompanied by obvious non-smooth renal envelope, protruding outward, and nodular mass. Patients should pay attention to a light diet and do not eat spicy and stimulating food. If the patient has any discomfort, please go to the regular hospital in time, according to the diagnosis results of the symptomatic treatment, so as not to delay the condition.