Petersen CG, Ovesen T, Pedersen CB. Acute mastoidectomy in a Danish county from 1977 to 1997-operati6e findings and long-term results. Acta Otolaryngol 2000; Suppl 543: 122-126.Data from patients undergoing acute mastoidectomy were examined retrospectively to evaluate if the nature of acute mastoiditis (AM) treated surgically has changed during the last 20 years (1977 -97). Moreover, a prevalence study was conducted to clarify the otological and audiological course following acute mastoidectomy. Patients with cholesteatoma and intracranial complications were excluded. Thus, 79 patients with a median age of 16 months were included. Thirty-seven percent had a history of middle ear disease, and the mean duration from onset of symptoms to admission was 9 days. Well-being was affected in 46%, and 82% had fever. The clinical picture was dominated by auricular protrusion (77%) and pathological tympanic membrane (94%). Postauricular oedema, hyperaemia and tenderness were demonstrated in 89%, 78% and 49% of cases, respectively. Peroperatively, purulent middle ear effusion was recognized in 92%, subperiosteal abscess in 66% and pus in the mastoid in 90%. Specimens revealed growth of pathogens in 58%, predominantly Gram-positive bacteria. The observation period was 1 -20 years. The findings in operated ears were not significantly different from the contralateral non-operated ears concerning incidence of otitis media, hearing and ear canal volume. Conclusively, acute mastoidectomy is a safe and effective treatment to eliminate infection. The operation can be done with negligible risk and does not leave long-term sequelae. Key words: acute mastoidectomy, long-term results, operati6e findings.