Considering the general impression of an increased number of patients with acute renal colic, the frequencies of roentgenologically verified ureteral and kidney calculi in a Swedish urban district have been studied for the periods 1953-55 and 1968-70. In a material of 986 outpatients (793 men and 193 women) we have proved an increase in incidence for upper urinary tract calculi in men from 2.2 to 3.3 0/00 (p less than 0.001) and in women from 0.5 to 0.8 0/00 (0.01 less than p less than 0.05). For the material as a whole, we have found a 50% increase (from 1.3 to 2.0 0/00; p less than 0.001) of acute urolithiasis between the periods studied. Some implications of the results in connection with primary hyperparathyroidism are discussed.