In the paper the principal data on bionomy, ecology, etology and harmfulness of Cameraria ohridella are given. The moth has regularly damaged parks trees Aesculus hippocastanum since 1994 within the territory of Slovakia. It has 3 to 4 generations during vegetation period. In the picture there is shown its life cycle as well as duration of the single developmental stages. The harmfulness of single larval stages expressed as percentage of leaf mined area from the total leaf area was measured by planimetry during a vegetation period. According to the obtained data on pest etology, we suggest protective measures against Cameraria ohridella - manual protection based on raking out fallen leaves and their burning or composting and single chemical treatment of horsenut trees in the period of eggs ovoposition and occurrence of first generation imagoes by insecticides on the basis of morphoregulators or in the period of occurrence of all developmental stages spraying by insecticides with combined contact and systemic effect. Designed control was tested in practice in the years 1999 - 2000, when 8000 horsenut trees were treated.