We studied the consequences of nest predation and brood parasitism on a population of Wilson's Warblers (Wilsonia pusilla) breeding in coastal riparian woodlands in northern California. We monitored 90 warbler nests from 1997 to 2000; only 16 of these produced Wilson's Warbler young. Of 74 failed nests, 73% (54/74) failed due to nest predation. Overall, 33% (30/90) of the nests were parasitized by Brown-headed Cowbirds (Molothrus ater). Nest success, as calculated by the Mayfield method, was 0.085 and notably lower than values reported for other warbler species. We used a simple demographic population model—under scenarios of high, average, and low productivity and survival—to evaluate the viability of this population and found it to be at risk of local extirpation without immigration. This was due to the combined effects of high levels of nest predation and the impacts of brood parasitism.