Variation at 15 microsatellite loci was surveyed in summer run steelhead trout (Oncorhynchus mykiss) from 16 populations in the Skeena River drainage. Genetic variation has been examined for Skeena steelhead since 1998; in 2009, a further 900 samples from the Tyee Test Fishery were analyzed from tissues collected in 2007 and 2008. The objective of this investigation was to further resolve/describe Skeena summer steelhead stock composition and abundance. Analysis of simulated mixed-stock samples suggested that variation at the microsatellite loci provided relatively accurate and precise estimates of stock composition for fishery management applications. Microsatellites provided an effective way to determine population structure, and provided reliable estimates of stock composition in mixed-stock fisheries; run timing and stock composition information is provided for Skeena summer steelhead captured at the Skeena estuary in a gillnet test fishery in 2007 and 2008.