Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic disease, affecting a half million Americans. The clinical phenotype can result from at least two different gene defects. One gene that can cause ADPKD has been located on the short arm of chromosome 16. This discovery has made possible new methods for diagnosing the disorder in gene carriers prior to the development of renal cysts. Although renal cysts are clearly an important manifestation of the gene defect, other systemic manifestations are both common and clinically important. Cardiac valvular lesions, intracranial aneurysms, hepatic cysts, and diverticula are included in the array of systemic manifestations. Moreover, renal cysts are only one of a myriad of renal manifestations. Although ADPKD was long considered an adult cystic disease, it is also a common cause of childhood cystic disease and must be considered in the differential diagnosis in that setting.