We studied the dental records of British military personnel who were less than 20 years old on enlistment, and had at least five years' service with at least five recorded dental inspections, at three military dental centres in the UK. The median (IQR) period from first to last inspection in 720 subjects was 15 (10-19) years, and the median frequency of inspection was every 14 (13-16) months. A total of 288/1250 mandibular third molars were extracted (23%). There were significant increases in the proportion of extractions stating caries in the mandibular third molar or multi-episode pericoronitis as indications (n=13, 14%, p <0.001) (n=15, 19%, p <0.001) post-introduction of NICE guidance. The number of extractions with no documented indication was reduced by 50 (26%, p<0.001) and that for a single episode of pericoronitis by 20 (9%, p =0.02). Extractions of mandibular third molars because of caries in the adjacent second molar increased by 4 (4%, p=0.045). The median age at the time of extraction before introduction of the guidelines was 23 years compared with 25 years afterwards (p<0.001). Twenty-five of 114 (22%) extractions of mandibular third molars were in patients over the age of 30 after the introduction of guidelines compared with 1/174 (<1%) before. The introduction of the NICE guidelines on the management of third molars has significantly changed our practice. Whether or not these changes have resulted in a net benefit to patients is still a matter for debate.