Actinomycosis involving the colon is rare. The aim of the present article is to report an additional case of this rare entity. A young female has been operated upon for suspected presence of sigmoid neoplasm. A mass involving the sigmoid colon, the apex of the urinary bladder, the fundus of the uterus and the left adnexa was found. En-block resection was performed. Histological examination confirmed the diagnosis of actinomycosis. Most of the cases of colonic actinomycosis were diagnosod postoperatively. Whether more accurate preoperative diagnosis should be possible in the future is still an unanswered question.