We describe a prolonged diagnostic process of 7 months before an infection with Actinomyces species could be diagnosed. Initially, a malignant tumour of the pelvic area was suspected. The patient underwent 3 CT-scans, 4 ultrasound scans and 5 biopsies before the diagnosis was suspected. Only the fourth microbiological investigation could confirm the diagnosis. This case emphasizes the necessity of microbiological examination of biopsies, when a tumour is found and malignancy cannot be confirmed, and is a reminder of Actinomyces species as an important pathogen in such cases.