Läckö Castle is an historic building that has never been permanently heated but has been dehumidifiedsince the early 2000s to house museum collections. The purpose of the work was to evaluate thedehumidification performance and compare the climate with the state of preservation of wooden wallpaintings. Compiled climate recordings for different rooms in the castle from 1997 to 2009, before andduring dehumidification, were used and compared to the outside climate. The RH set point value of 70 % for dehumidification was not reached often, especially in winter with high outside RH. Wood painted witha linseed oil paint performed well, whereas paint containing resin was seriously damaged. It is concludedthat microclimatic differences in relation to dominating wind direction are important. The air exchangeof the building is very decisive for dehumidification efficiency.