A postoperative symptom severity (PoSSe) scale was devised from questions commonly used in the clinical assessment of patients who have had third molars extracted, and divided into subscales corresponding to seven main adverse effects that had been identified in a previous study. Ninety-seven patients completed the 15-item questionnaire at one week, and 71 patients at four weeks, after extraction of impacted third molars. After statistical testing, four items were discarded and the final PoSSe scale achieved a high level of internal reliability. Patients' PoSSe scores were highly correlated with scales that measured six distinct health dimensions. The level of social functioning, together with the number of impacted teeth and number of painkillers taken, explained 62% of the variation in PoSSe scores between patients one week postoperatively. The PoSSe was more responsive than the Short Form 36-item Health Survey. In conclusion, we found the PoSSe Scale to be a reliable, valid and responsive measure of the severity of symptoms after extraction of third molars, and of the impact of those symptoms on patients' perceived health. (C) 2000 The British Association of Oral and Maxillofacial Surgeons.