The article presents the research results of the damage scale of trees at forestry works with the use of specialistic machines. The research was carried out in Rokita Forestry Management, Regional Management of National Forests in Szczecin. The effects of using cutting and logging machines were taken into account. The works were carried out in thinning forest stand. Based on the obtained results it was found out that the biggest damage concerning the number are generated by harvesters during cutting trees. Damage concern the exposed tree alburnum in the amount of 57 item·ha -1. At the logging works with the use of forwarder 4 item·ha -1 of broken branches were reported. Number of damage was decisively higher at the works performed in a late positive thinning, where there were no skidding roads. In thinning, where technological roads were used, the number of damage decisively decreased. Technological parameters of machines were not adjusted to technological parameters of the forest stand in 50%.