A total of 1,055, scale samples from tagged, recaptured brown trout, rainbow trout, and brook trout and 129 scale samples from planted, marked rainbow trout were taken from Prickley Pear Creek, Montana, between June 1949 and October 1951. In addition, scale samples were obtained from 69 rainbow trout planted as fry in Savage Lake, Montana, and from 42 known-age rainbow trout of the brood stock at the U. S. Fish and Wildlife Service Fish Hatchery, Ennis, Montana. Studies of these scales substantiated the general validity of the scale method of aging wild trout and trout planted as fry or young-of-the-year fingerlings.