We conducted a mark-recapture study of three subpopulations of Craugastor punctariolus at a mid-elevation site in central Panama between 1999 and 2005. The study spans a period over which the pathogenic fungus Batrachochytrium dendrobatidis (Bd) was absent from the site, invaded the site and decimated all amphibian populations, and now persists. We quantified natural demographic parameters prior to and during an event of mass mortality due to chytridiomycosis caused by Bd. Prior to the event of mass mortality, all three subpopulations of C. punctariolus were large (19-68 animals/200m), showed a stable age-size distribution, and had high survival. All age-size classes of this species co-occurred on boulder clumps along streams, and adults showed high site fidelity and were likely territorial. Following detection of Bd at this site in late September 2004, four dead C. punctariolus were found infected with Bd and all three subpopulations completely disappeared from this site within 2months. The association of all age-size classes with microhabitats appropriate for survival and growth of Bd likely contributed to the rapid and severe degree of decline of this species at this site. These data provide insight into the patterns and mechanisms of decline within a species due to Bd.