INTRODUCTION: The indigenous populations of the Arctic are prone to middle ear infections starting with an early age first episode, followed by frequent episodes of acute otitis media (AOM) during childhood. A high proportion develop chronic otitis media. Acute mastoiditis is a serious complication of AOM in childhood with postauricular swelling, erythema, and tenderness, protrusion of the auricle, high fever and general malaise. The disease may protrude intracranially. The incidence rates for acute mastoiditis in the Western world range from 1.2 to 4.2 cases/100 000 per year. There exists no epidemiological data on acute mastoiditis in the Arctic region. METHODS: A retrospective search was made for the WHO ICD-10 code DH70.0 (denoting acute mastoiditis) using the National Greenland Inpatient Register for the period 1994-2007, inclusive. Fifteen patients were registered and their medical records were retrieved. Four patients were obviously misclassified, leaving 11 patients for evaluation. The medical records were available for 10 patients. The diagnostic inclusion criterion was written clinical signs of acute mastoiditis. RESULTS: Based on the case series the incidence rate was calculated to be 1.4 for the total Greenlandic population and 7.4 for children 0 and 10 years of age. Median age was 14 months (5-105 months) and eight were female (72%). Seven of the 10 were exclusively treated with antibiotics and three underwent additional ear surgery. Bacteriological examination was performed in five of 10. One 8 month-old girl presented with a contemporary facial nerve paralysis and was treated with intravenous antibiotics; one 8 year-old girl was evacuated to Copenhagen for urgent surgery due to signs of meningitis. Acute CT scan showed a cerebellar abscess and a thrombosis in the lateral sigmoid sinus vein. An extensive cholesteatoma was found and eradicated during surgery. Six weeks later the patient returned home with a maximal conductive hearing loss as the only complication. All patients recovered from the disease. CONCLUSION: The incidence of acute mastoiditis in Greenland is comparable to the incidence elsewhere, although AOM occurs more frequently among small children in the Greenlandic population. The disease is serious and must be treated immediately with intravenous antibiotics, followed by urgent surgery if there is no improvement.