Abstract The paper presents a study regarding the aggregations of the Lesser Horseshoe bat Rhinolophus hipposideros in Latium, Central Italy, based on data collected during 27 years in natural caves (limestone) and artificial buildings (abandoned mines, ancient monuments and others). Furthermore some parameters including size, dynamics, sex ratio and age structures are investigated. The number of bats that occur at the hibernacula in winter is low over the whole territory of this region, the most numerous aggregations being 18 individual bats with an average of about 4 bats/visit. In the shelters of the area, the highest numbers of R. hipposideros, a stenotherm thermophilous species, is reached at the end of January, while at the beginning of spring (April) few bats are generally observed. As in many other European populations, males are more commonly represented in winter samples; some caves harbour only adult males over a long time span, about 20 years. The results would suggest that some conservation measures should be introduced to protect this widespread but uncommon and threatened species.