Rates of recapture as grilse of salmon tagged as smolts at two counting fences located 7 and 40 miles above tidehead on the Northwest Miramichi River, New Brunswick, were from 2.5–3.8%. The Northwest Miramichi has early (June–July) and late (September–October) runs of grilse and larger salmon. In this study, returns by and after August 16 are described as early and late respectively. Grilse returns from smolts produced in the headwaters (and tagged at the upper counting fence) were mainly in the early run. Smolts marked at the lower counting fence (but produced in all parts of the river above lower fence) were well represented in both the early and late runs of grilse. Of grilse ascending past the lower counting fence by August 16, a higher percentage of those tagged as smolts at the upper fence than at the lower fence reached the upper part of the river. Of the tagged grilse which ascended past the lower counting fence after August 16, none were recaptured in the upper part of the river. Times of smolt migration to sea and return of grilse appeared to be related to smolt age. Older smolts (age 3 and 4) tended to migrate earlier than younger ones (age 2). Grilse from older smolts were nearly twice as numerous in the early as in the late run; those from younger smolts were nearly equally represented in the early and late runs.