Ancient trees are important habitats, confer vital ecological roles and function as cultural legacies. Old trees with large girth are keystone structures in various ecosystems. We aim to present which species amongst the greatest Hungarian trees (and some other phanerophyte plants) are damaged by polypores (the most important agents of wood decay), Agrobacterium tumefaciens (usually causing root tumour) or ivy (competing against the native vegetation and causing windthrow damage) and at what extent and frequency; and whether there is a relationship between these types of damage and the origin of the species (native or adventive) or its situation (solitary or surrounded by other trees). We measured 2,000 trees, belonging to 29 native and 43 non-native species. Polypore infection could be detected in 12.2% of the observed 531 settlements, 22.8% are damaged by Agrobacterium and 29.6% by ivy, while 51.2% by other types of pests and diseases. Altogether, one third of the observed 2000 ancient or veteran trees suffered from one or more types of damage. A total of 33.5% of the native species (519 specimens out of 1550) and 28.7% of the adventives (129 trees out of 450) are damaged by any (or more than one) of the mentioned infections or ivy. Mostly, damage occurred to those old trees that stand in a park or forest, while the single (solitary) trees were usually healthy. The most infected regions are the western and south-western counties, while the Northern Hungarian Mountain Range is much less affected, despite its great sample size. Low damage was detected in the Great Hungarian Plain, but the number of sample areas and veteran trees was also low here. The damage to old trees remains without any management or healing in Hungary, since the only effective solution would be prevention.