The seasonality and diversity of members of the beetle family Leiodidae were determined for an old-growth and a 40-yr-old forest in New Hampshire. Thirty-four species were found at each site for a combined total of 39 species. Diversity was calculated using log series index α, Shannon-Wiener index, coefficient of community, and percent similarity. Seasonality is lengthily unimodal for the Cholevinae, which feed on carrion and fungi. The Leiodinae feed on slime molds and fungi and are more narrowly unimodal.Anisotomaspp. exhibit broadly overlapping abundance peaks, whereas some members ofAgathidiumandLeiodeshave abundance peaks at different times, indicating the possibility of resource partitioning. The greater leaf litter depilis and amount of woody debris at the old-growth site are presumed to lead to the production of more food resources for the leiodids. The difference in forest ages and the disturbance by selective cutting has not lowered species richness, but the diversity indices used reflect a difference between the sites based on greater abundance in the old-growth forest. The dispersal ability of leiodids is presumed to lead to rapid recolonization of the younger forest as food sources become available.Anisotoma inopsBrown is a potential indicator species for old-growth forests in northeastern North America.