The abundance of medium and large chinook salmon Oncorhynchus tshawytscha that returned to spawn in the Unuk River in 1998 was estimated using a two-event mark-recapture experiment. Fish were captured in the lower Unuk River using set gillnets from June through July, and each healthy fish was individually marked with a solid-core spaghetti tag sewn through its back and was given two secondary batch marks in the form of an upper-left operculum punch and removal of the left axillary appendage. Spawning grounds sampling took place from July through August to estimate the fraction of the escapement that had been marked. During this study, 610 chinook salmon were captured in the lower Unuk River, and 555 of these were marked and released alive. Of the marked and released fish, 466 were considered large (660 mm mid eye to fork [MEF]), 87 were medium (401659 mm MEF) and 3 were small in size. On the spawning grounds, 924 fish were sampled; 707 were considered large fish, and of these, 79 were recaptures that had been previously marked in the lower river with spaghetti tags. Two hundred seventeen (217) medium fish were sampled, and 15 of these were recaptures. Thirty-two (32) small fish were sampled, of which 2 were age-1.0 fish (mini-jacks), 225 mm and 250 mm MEF in size. A modified Petersen model was used to estimate that 4,132 (SE = 413, = 466, = 707, = 79) large, 1,198 (SE = 290, = 87, = 217, = 15) medium, and 5,330 (SE = 497) fish >400 mm MEF in length immigrated into the Unuk River in 1998. An estimated 27% of this immigration was sampled during the project. Peak survey counts in August totaled 840 large chinook salmon, about 20% of the mark-recapture estimate of large fish, a trend seen in similar studies. Of the spawning population >400 mm MEF, 49% were estimated to be age-1.3 fish from the 1993 brood year, 23% were estimated to be age-1.4 fish, and 24% were estimated to be age-1.2 fish.