INTRODUCTION: Actinomycosis is a rare infection caused by Actinomyces spp. which are part of the oral, intestinal and vaginal bacterial flora. It can invade tissue through mucosal disruption and form abscesses which tend to be difficult to treat and diagnose. This population-based study explores the epidemiology and manifestations of actinomycosis in Iceland. METHODOLOGY: All diagnosed cases of actinomycosis in Iceland 1984-2007 were identified by a computerised search using ICD and SNOMED codes. Clinical information was collected by chart review. The subjects were included in the study if they fulfilled two out of five diagnostic criteria. RESULTS: 41 women and 25 men (mean age 45 years) met the diagnostic criteria. The incidence rate during the first half of the period was 0.86/year/100.000 and 1.17 during the second half.The cervicofacial region (42%) was most commonly affected, then the pelvis (32%), lacrimal duct (14%), abdomen (11%) and thorax (2%). Diagnostic delay was common. The longest delay from first symptoms to diagnosis was 8-9 years (median 5 months) and it was significantly shorter among patients with abdominal or pelvic infections compared to infections of the lacrimal duct (p=0.012). No significant difference was noted in diagnostic delay between other groups and no patients died from the infection. CONCLUSION: This is the first population-based study of actinomycosis. The incidence rate increases with age and the time passing from first symptoms to diagnosis tends to be long.