Poplar species such as aspen (Populus tremula L.) play a very important role in the forest formation process not only in Eastern European regions. Unfortunately, such aspen stands are often severely affected by fungal diseases, causing mainly core rot. In this study, the indirect effects of thinning on the phytosanitary condition of aspen by pro- motion of tree growth were investigated. Two thinning methods, manual (thinning from below) and mechanical thin- ning (schematic), were applied to young stands dominated by Eurasian aspen to study their effects on tree growth and health. All trees were measured at breast height and diameter frequency distribution was determined twice, i.e. three and 24 years after the beginning of the experiment. In addition, during the second measurement, tree-ring samples were obtained from individual trees to evaluate growth and wood decay damage. Neither manual nor mechanical thin- ning of aspen significantly increased its growth at the stand level, but positive effects on individual trees were observed in plots where mechanical thinning was applied. The thicker the trees, the less decayed they were. The analysis suggests that thinning in general should not be used to increase stand production, but the positive effects of mechanical thinning on individual aspens can be recommended to promote the growth of individual vigorous trees.