We describe nest-site selection and report measures of breeding productivity from a population of Song Wrens (Cyphorhinus phaeocephalus) in central Panama. We studied 31 pairs from 1995 to 1998 and collected data on nest predation from 1996 to 1998. Song Wrens are year-round residents that build breeding nests for reproduction and dormitory nests for roosting. Twenty-five of 50 Song Wren breeding nests produced fledglings (daily nest survival rate = 0.968). Song Wrens usually (78%) placed their breeding nests in ant-defended acacias (Acacia melanoceras). However, nests placed in acacias did not experience lower rates of nest predation than nests placed in sites not defended by ants. The population-wide breeding season was seven months long, but individual pairs often bred within a span of only 2.5 months. Modal clutch size was two (n = 42), but the frequency of three-egg clutches was high (≥27%). Pairs that lost eggs or chicks renested more quickly than pairs that fledged young and attempted a second brood. Observed annual production of young was 1.4 fledglings per pair. Compared with other wrens, Song Wrens had a much longer breeding season and longer intervals between broods. The annual productivity of Song Wrens was the lowest recorded for any wren, which may have been due to smaller clutch sizes, long intervals between broods, and the correspondingly low number of nesting attempts per pair per year.