Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the unrelenting enlargement of innumerable cysts derived from renal tubules. This cystic growth often leads to a grotesque renal enlargement. Relatively early in life, the cysts trigger secondary complications including pain, hypertension and gross hematuria; renal insufficiency is usually not detected until the fifth or sixth decade of life. Therapies targeted to molecular and pathophysiological abnormalities slow cyst growth and protect renal function in animal models of the disease. Unfortunately, the translation of these treatments into clinical trials is hampered since glomerular filtration rate, the usual biomarker of renal disease progression, does not decrease substantially until extensive and irreversible damage to noncystic parenchyma occurs. Ultrasonography, CT and MRI have been used for many years to quantify the increase in renal volume in patients with ADPKD. Imaging with these techniques has also been used to accurately quantify the rate of increased kidney and total cyst volume in patients. In this Review we discuss the overwhelming evidence in support of the view that imaging is an invaluable tool to monitor the onset and progression of ADPKD and is well-suited to gauge the response of this disease to targeted therapy before renal function begins to decline.