In natural forest reserves (NFR), forests develop in the absence of direct human interference, primarily management. This increases their naturalness and should – in the long run – allow forests to regain primeval attributes. Based on stand structural data from the third National Forest Inventory (NFI) and 25 NFR in Switzerland, we investigate 1) whether NFR feature more naturalness than managed forests, 2) whether the naturalness of Swiss forests increases with the time elapsed since the cessation of management, and 3) to what extent NFR differ from Swiss forests that have not been managed during several decades. Thereby, we focus on the four main forest types beech, silver fir-beech, silver fir-Norway spruce and Norway spruce forests, and furthermore group the data according to the time since the last intervention (0–20, 21–50 and > 50 years.). The structural features investigated differ only slightly between NFR and managed forest (0–20 years). NFR feature a higher abundance of "giant" trees (dbh ≥ 80 cm), higher stem numbers and greater basal area, and thus a higher growing stock. The abundance of snags, however, is indistinguishable between the two types of forests. Naturalness in Swiss forests increases only slightly with time since the last intervention, indicated by a higher abundance of small snags and a slightly higher number of giant trees. By contrast, clear differences can be seen between NFR in which no intervention has taken place for at least 50 years, and other forests abandoned for a similarly long time, with NFR showing lower stem numbers, greater basal area and higher numbers of giant trees. Many of the investigated reserves are still affected by former management and are – from the point of view of primeval forest dynamics – still quite "young". According to their naturalness, the NFR range between managed and primeval forests, although to date they are still closer to the former. Nevertheless, the differences found in our study indicate a steady development of the NFR towards stand structures that are characteristic of primeval forests.