The methodology of age determination from scales of chum salmon (Oncorhynchus keta) is reviewed. Scales from chum salmon caught in the North Pacific Ocean and streams of North America were studied. Most annuli are of two main types: a poorly formed circulus usually "cut over" by the first circulus of new growth, and what appears to be a normal circulus in the annual ring. The annulus of type 1 may be independent of the annual ring. Annuli may be at the anterior or posterior margins of the annual ring, or within it. Direct evidence that annuli are recognizable age indices was obtained from scales of marked fish.An average of 98% of the age determinations by three scale readers agreed with the known age of the fish. The time of annulus formation or start of new growth extends from as early as March to the end of June and possibly to the end of July. The annual ring begins to form near the end of the season (as early as August) or when new growth occurs in the spring or summer. Sometimes an annual ring is not formed. Scales taken from various parts of the body had the same number of annuli.