Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary renal disease. New data from Paul et al. suggest that mutations in the PKD1 and PKD2 genes may account for all cases of ADPKD. Further improvements in mutation detection methodologies are needed to determine the true relative frequency of PKD1 versus PKD2 as well as to establish the value of mutation type and location to predict disease severity in this disorder.