Logging and modern forest management reduced the frequency of key features of old-growth forest, especially old, dying and dead trees in the Scandinavian boreal forest during the 20th century. To quantify the decline and spatial differences, we have analysed density changes of old trees between 1926 and 1996 on a regional scale (approximately 50,000 km²) in boreal Sweden. The occurrence of old-conifer trees (+159 years) has dramatically decreased in the studied area and today only one third as many old Scots pines (Pinus sylvestris L.) and Norway spruces (Picea abies (L.) Karst.) can be found as in the 1920s. However, the density of old deciduous trees (+99 years) has not decreased since the early 20th century. Historical baseline data such as these are needed for modern forest management, conservation programmes and ecological restoration projects. Existing old trees are very important for biodiversity, and may also preserve elements of cultural heritage from pre-industrial times.