We provide the first description of the nest, eggs and nestlings of Sharpe's Wren ( Cinnycerthia olivascens ) from northeastern Ecuador, and we document the occurrence of cooperative breeding in this species. Cinnycerthia olivascens builds large enclosed ball nests with a downward-projecting tubular entrance. The eggs are off-white with sparse reddish-brown speckling. We show that at least three adults may participate in nest-building and probably contribute to nestling provisioning. Our video observations document fledgling and show that the nestlings' diet consisted of small invertebrates.