This study investigated disturbance patterns of a Fagus sylvatica virgin forest remnant based on an inventory of the horizontal canopy structure. Stand data were collected from the Krokar reserve in the Slovenian Dinaric Alps. The canopy layer was classified in gap and non-gap areas based on the terrestrial inventory, and compared with aerial photography interpretations. The study identified 49 canopy gaps, which covered 5.6% of the reserve area. Gap size varied from 6 to 833 m², with a mean value of 137 m². Gap size frequency at 50 m²-class intervals followed the too-normal distribution. Single-tree gaps were predominant and the directions of the main gap axes were randomly distributed. Considering the canopy dichotomously as gap and non-gap areas proved to be a suitable procedure to analyse gap dynamics in one-layered, beech-dominated virgin forests. Gap formation was influenced by a combination of both endogenous and exogenous environmental factors. Saprophytic fungi and wind were the main components of the disturbance regime. Gaps were relatively small and they occupied a small land area. These features may be attributed to interactions between climate, landform, rich soils, disturbance regime and the ability of beech to close gaps by lateral branch growth.