The authors assess the predictive accuracy of population viability analysis (PVA), as well as comparing different generic PVA computer packages for their predictive capabilities. PVA is used to predict extinction risks for threatened species and to compare alternative options for their management. However, because of its lack of validation in real systems, there is considerable skepticism regarding the predictive accuracy of PVA. Twenty-one long-term ecological studies were used to conduct the study. Authors found that PVA predictions were surprisingly accurate. Computer simulations closely matched observed outcomes, no significant bias was recorded, and population size projections did not differ significantly from actual numbers. They also found that the five PVA software packages were highly concordant, and conclude that PVA is valid and sufficiently accurate for catagorinzing and managing endangered species.