In recent years, our knowledge on the pathophysiology of polycystic kidney disease expanded dramatically. An increasing number of genes mutated in renal cystic diseases in humans or rodents have been identified and most of them encode proteins that localise in the primary cilium, a mechanosensor that regulates intracellular [Ca2+]i levels. Polycystin-1 and polycystin-2, the proteins encoded by the genes mutated in patients with autosomal dominant polycystic kidney disease (adpkd), seem to play a crucial role in this regulation. The polycystins belong to a novel subclass of transient receptor potential (trp) channels, the transient receptor potential polycystins (trpp's). Increased knowledge on altered signaling in polycystic kidney disease and the availability of a variety of animal models are now providing the opportunities to test therapeutic interventions.