Cystinuria is an inherited disease that has been long recognized in dogs and has been documented in nearly 70 breeds. Our previous studies made significant progress with a form of cystinuria that is clinically manifested at an early age such that we can go from seeing an affected animal in the clinic to a DNA-based test in a matter of weeks. We now have access to sufficient pedigrees to make similar progress for cystinuria that presents at a later age, and probably represents a more common form of the disease. Genetic testing is even more important for a disease that has a later age of onset.