The 'Akiapola'au (Hemignathus munroi Rothschild) is an endangered Hawaiian honeycreeper that is found only in high-elevation native forests on the island of Hawai'i. The Hawai'i Forest Bird Surveys (HFBS) during 1976-1979 on Hawai'i found four disjunct populations of 'Akiapola'au totaling 1500 ± 400 (95% CI) birds. This total included 533 ± 320 in the Ka'u Forest Reserve and 46 ± 51 birds in dry mamane (Sophora chrysophylla [Salisb.] Seem.) forest on Mauna Kea. Because 'Akiapola'au are so rare, it was necessary to use data for other species to determine the effective area surveyed for 'Akiapola'au and to use data interpolation and smoothing techniques to derive the HFBS estimate of 1500 'Akiapola'au. We used a newly developed analysis approach to estimate the population size for 'Akiapola'au based on surveys conducted during 1990-1995. We plotted all recent detections of 'Akiapola'au and stratified the current distribution of the species based on distribution of koa (Acacia koa A. Gray) forests and elevation contours. A population estimate was derived by multiplying the density of 'Akiapola'au within each stratum, as determined from variable circular plot counts, by the area within each stratum. We estimate that there are 1163 ± 54 (90% CI) 'Akiapola'au in the world. The distribution of 'Akiapola'au has been greatly reduced in the Ka'u District, where the estimated population has declined from 533 to 44 birds, and relic populations in mamane forest and South Kona are likely to become extinct within the next 5 yr. Protection and management of the remaining isolated stands of koa forest at higher elevations where mosquitoes are absent or occur only seasonally are critical to the survival of this species.