A large family tree of polycystic kidney disease in 4 generations is presented. There are 14 positive members in a family of 41 members. The hereditary trait is carried as a dominant characteristic and is not sex linked. Incidence is equal in the 2 sexes. All but one member with the disease died between the ages of 40 and 60 yrs. Onset of symptoms may be early and consist of backache, intermittent hematuria, palpable masses in the abdomen. The kidneys reach enormous size, some weighing over 2,000 gms.