Branch and main stem defects of horsechestnut trees (Aesculus hippocastanum L.) in Pripyat, Ukraine, abandoned in 1986, and un-maintained since then, were compared to managed trees of the same species and similar age in the city of Kiev, Ukraine. Trees in Kiev sustained more trunk injuries, and numerous pruning wounds, and developed significantly more branch defects (especially codominant stems) in their canopies compared to trees in Pripyat. Although Kiev trees had larger stem diameters, the overall quality of their form was reduced compared to street trees in Pripyat. Pripyat horsechestnuts grew with competition from other, invading trees thus, experienced shading of their lower canopies and significant competition for light and had smaller bole diameters. Effects of the Chernobyl nuclear disaster on trees in the Nuclear Exclusion Zone are also discussed.