Riparian woodlands of aspen (Populus tremuloides) provide valuable breeding habitat for several cavity-nesting birds. Although anecdotal information for this habitat is available for Lewis's Woodpecker (Melanerpes lewis), no study has previously examined the importance of aspen woodlands to this species' breeding biology. From 2002 to 2004, we monitored 76 Lewis's Woodpecker nests in aspen riparian woodlands of south-central Idaho to describe nest-site characteristics and estimate the nests' survival. We quantified the vegetation at nest sites and randomly selected other sites to determine habitat features important in the species' selection of a nest site. We then related these features, as well as several time-specific covariates, to nest survival. Lewis's Woodpecker selected nest trees that were larger in diameter than random trees and selected nest sites with more trees, fewer woody stems, and less bare ground than random sites. However, nest-site characteristics were not important determinants of nest survival. Rather, nest-initiation date and daily maximum temperature had the strongest influence on nest survival, which was higher for early nesters and increased with increasing daily maximum temperature. Nest survival (74%) and productivity (2.3 fledglings per successful nest) were comparable to values observed for Lewis's Woodpeckers in burned pine forests, suggesting that aspen riparian woodlands also serve as valuable breeding habitat for this species in the Intermountain West.