Renal epithelial cysts are caused by hereditary or acquired etiologies of undetermined molecular mechanisms. The cysts develop within renal tubules by pathogenetic processes that involve cellular proliferation, accumulation of tubule fluid within distended cavities, and remodelling of extracellular matrix. Evidence is accumulating to support the view that renal cysts are composed of moderately dedifferentiated, immature epithelial cells that proliferate abnormally and transport solute and fluid by secretion, in contrast to the usual absorptive movement of liquid in normal renal tubules. The formation and expansion of renal cysts occurs in conjunction with alterations in the extracellular matrix, including thickening of the tubule basement membrane, infiltration of the interstitium with mononuclear inflammatory cells, and interstitial fibrosis. The pathogenetic elements of cyst formation are understood well enough that it is reasonable, and of considerable importance, to examine in animal models treatment strategies that may be hypothesized to allay the progression of cystic disease to end-stage renal failure.