Abstract The following paper contains data on nest-box occupation by the dormouse in four habitats of the Presidential estate of Castelporziano. Dormouse has been observed inside the nest-boxes in all months of the year and active animals have been repeatedly observed during the winter. These results concord with suggestions that in the Mediterranean area the species occupies nest-boxes also in winter and that it has different yearly rhythms of activity than in northern areas. Except in pine woods, the dormouse was found in nest-boxes of all study habitats. Some results seem to show that competition with hole-nesting passerines heavily affects spring occupation by the dormouse. In spring the Dormouse prefers 'old' nest-boxes, 'new' nest-boxes (i.e. at the first year of placement in a habitat or in a new area) are occupied at higher extent from the autumn onwards. Yearly variation in occupation percentages of nest-boxes by the dormouse were also observed.