We analyzed data from two beetle taxa, Pselaphinae (Staphylinidae) and Histeridae, collected during a seven-week expedition to Yasuni National Park (Napo Province, Ecuador) during June–August 1999. Smoothed species accumulation curves and richness estimators were used to assess the effectiveness of Berlese extraction, flight intercept traps, light traps, and a combination of other techniques in sampling these two focal taxa. From a total of 3,465 specimens, including 871 pselaphines and 2,574 histerids, we sorted 385 species, 178 pselaphine species and 207 histerid species representing 62 pselaphine genera and 63 histerid genera. We offer regional comparisons to assess the scale of diversity documented at Yasuni. Finally, we used these empirical data, richness estimates, and simple percentages to predict that beetle diversity at this site in Yasuni National Park ranges from 9,871 to 14,102 species, and total insect diversity ranges from 24,665 to 35,255 species.