If the right kidney becomes distended and painful, it is recommended to go to the hospital for further examination. The possible causes are: 1. Right kidney stone, when the stone obstructs the ureteral junction of the renal pelvis, mild hydronephrosis can occur, and then the patient will feel distended and painful in the right kidney. With the further aggravation of obstruction, the degree of right kidney distension and pain can be further aggravated, and ultrasound examination of the kidney is needed to rule out the presence of kidney stones. 2. Right ureteral stones can also cause mild hydronephrosis in the right kidney. With the further aggravation of the obstruction and the degree of fluid accumulation, the patient will experience a significant increase in right kidney distension and pain. It is necessary to perform further urological ultrasound examination to find out whether there are ureteral stones. 3, pyelonephritis, when pyelonephritis occurs, the patient can have swelling and pain in the right lumbar area, and accompanied by symptoms such as chills, high fever, urinary frequency and urinary urgency, etc. It is necessary to take urine for routine examination and culture check, if there is infection, combined with the symptoms can be considered as pyelonephritis.