Multicystic dysplastic kidney (MCDK) is a type of congenital kidney abnormality where the kidney is completely replaced by multiple cysts held together by connective tissue like a bunch of grapes. The ureter is often atretic or absent, and the cysts usually do not communicate, distinguishing MCDK from hydronephrosis. Nowadays, 47% of cases occur prenatally, while 30% of cases present with a lateral mass, 5% with urinary tract infection, and 18% with other symptoms. Males are more commonly affected, and there is a slight left-sided predominance. To diagnose MCDK, a renal ultrasound is usually performed, which shows characteristic features that distinguish it from hydronephrotic kidneys. A renal scan such as DMSA or MAG-3 is usually obtained to confirm the diagnosis and evaluate the contralateral kidney. In some cases, a nuclear cystogram or voiding cystourethrogram is also recommended to evaluate for contralateral vesicoureteral reflux. If MCDK is detected prenatally, it is important to assess the amount of anti-kidney and amniotic fluid. In rare cases, surgical exploration is required if the diagnosis is inconclusive despite radiological workup. Treatment for MCDK is controversial. While some advocate surgical removal of the affected kidney, others prefer observation. Leaving the kidney in place carries a risk of hypertension (rare) and renal tumors, but the risk is low with only six reported cases. If the kidney is left in place, patients should have an annual renal ultrasound and blood pressure measurement. In general, MCDK patients do well with one kidney because bilateral disease is rare.