The absolute size, N, of a Dolichopoda geniculata population was estimated both by the Lincoln-Petersen index and the total count on sample plot methods in a natural cave in Central Italy. 19 pairs of estimates, obtained over 2 years, exhibit a seasonal pattern and a mean value of N ≈ 430. Differences between estimates obtained with the 2 methods are not significant (P > 0.8). These results, and data from the literature enable most of the major factors influencing the two types of estimates to be identified. Respective cases where methods may be preferably applied are suggested.