Thirty 3–4 yr-old twigs were collected at each of three sampling dates between May 1995 and May 1996 from each of ten approximately 120 yr-old European beech trees in the Tuscan-Emilian Apennines to examine the bark for the presence of endophytic fungi. Five trees with low crown transparency ([les ]5%) and five trees with high crown transparency ([ges ]25%) were compared. Almost all of the 900 examined bark samples were colonized by endophytic fungi. More than 30% of the twigs appeared to host three or more fungal species. Forty-four endophyte species were detected. An Aposphaeria and a Cryptosporiopsis species, Botryosphaeria quercuum, Discula umbrinella and Neohendersonia kickxii occurred most frequently in all of the three samplings and seemed to play a dominant role as endophytes in beech bark. Significant differences in endophyte assemblages between trees with low and trees with high crown transparency could be detected only with respect to the Aposphaeria species. The colonization of tissues by this fungus, possibly a weak pathogen, was predominant on trees with high crown transparency.