The effectiveness of acetylation as a method to increase the durability of wood has been demonstrated in several studies over the last sixty years, starting with pioneers like Tarkow, Stamm and Goldstein. Nevertheless, as acetylated wood has now reached large scale production, the importance of long term-field test data on the performance of acetylated wood has increased. Firstly, this paper will address a project started in 1991, where acetylated Scots pine is tested in a full EN 252 test. The test is still running in Nordic NWPC test fields, Simlångsdalen in Sweden and in Viikki, Finland. The results show that irrespectively of test field, pine wood test stakes with an acetylation level of about 22% (expressed as acetyl content) were as durable as the CCA treated wood at a high retention level (10.3 kg/m3) after 15 years in ground contact. Secondly, acetylated wood (acetyl content 22%) is also being evaluated under marine conditions in Kristineberg on the Swedish west coast, according to EN 275 (marine borer resistance). The test has been running since 1999 and the X-ray rating shows a slight attack by marine borers after eight years in test, whereas the untreated controls failed after only one year. If the acetylation (acetyl content 21%) is followed by a post treatment with melamine resin (weight gain 19%) no attack could be observed after eight years. Thirdly, coated acetylated pine panels were exposed on rigs 45º facing south for 13 years, according to an early version of EN 927-3 in Ultuna and Malmö. The results indicate that acetylated wood in combination with a proper coating system, gives a considerably longer service life of the panels as compared to coated unmodified panels.