Population viability analysis (PVA) uses computer modeling to evaluate the influence of interacting demographic and stochastic factors on the survival probability of endangered species. I used the computer program, VORTEX, to examine the risk of extinction for the Hawaiian monk seal, Monachus schauinslandi, an endangered seal species found only in the Northwestern Hawaiian Islands. Because of long term monitoring efforts by the National Marine Fisheries Service, more data exist for this species than for many species for which population viability has been analyzed. Objectives of this study were to identify the probability of persistence to 30 and 100 years for the Laysan Island subpopulation, and to conduct a sensitivity analysis on key parameters that may affect population persistence. In addition, I examined the effects of metapopulation structure and current management activities on monk seal persistence at other islands and atolls. This analysis indicated that the Hawaiian monk seal has a high survival probability over the next 30-100 years. Actual declines observed in subpopulations, however, suggest that simulations may be too optimistic. Results of sensitivity analyses indicated that survival is the most important factor in the persistence of this species, which is in agreement with theoretical studies showing that growth rate of marine mammal populations is sensitive to adult survival. In addition, extinction risks for this species increased with increasing levels of environmental variation and with increasing frequency and severity of catastrophes affecting survival. The metapopulation structure of the Hawaiian monk seal reduced the amount of variation in mean population sizes and may be important to the persistence of the smallest population at Midway Atoll. The Midway population was also susceptible to inbreeding because of its small size. Simulations also suggested that a focus on subpopulation management is appropriate and that current management efforts augmenting depleted subpopulations were likely to increase mean population sizes at 30 and 100 years. Although VORTEX simulations identified mortality as a key factor to monk seal survival, population viability simulations do not explain why declines are occurring. PVAs tend to ignore ecological factors such as interactions with disease, predators or prey that may strongly influence population dynamics. In addition, interactions between demography and behavior are ignored, but may have significant effects for this species. Because these factors are not included, it is likely that the true risk of extinction for the Hawaiian monk seal is underestimated by the model. Several aspects of this PVA, including the use of average adult survival and reproductive rates, also may be unrealistic for this species. These problems with the VORTEX model suggest that species with substantial population data available, such as the monk seal, may benefit from models tailored to their specific population variables.