Pelvic actinomycosis is difficult to diagnose. In most cases, it is not diagnosed until after surgery. If this condition is diagnosed preoperatively, it can be treated in many cases. Three cases of actinomycosis are reported here. Three women with intrauterine devices (IUD) each presented with lower abdominal pain and pelvic mass, and elevated white blood cell count and C-reactive protein. Left salpingo-oophorectomy was performed for one the women. The pathological diagnosis was actinomycosis. For the other two women, a Gram or Papanicolaou stain of the IUD sample showed actinomycetes. They were discharged after intravenous administration of penicillin without surgery.