Despite the fact that colorectal polyps and solitary rectal ulcers may be present in conjunction with rectal prolapse, association between rectal prolapse and rectal cancer is very rare. As far as we could determine, there are only a few articles concerning rectal cancer in association with rectal prolapse in the literature. This case, a 63-year-old female patient, had suffered from a rectal prolapse since childhood and presented as a case of rectal cancer. At presentation, she complained of constipation and rectal bleeding for the previous six months. At physical examination there was a relaxed anal sphincter and a large reddish mass protruding via the anal canal when the patient strained. There was a fungating lesion in the upper left part of the rectal mucosa. An incisional biopsy was performed, the histopathological result of which was adenocarcinoma of the rectum. Changes in bowel habits, chronic constipation and chronic irritation seen in rectal prolapse may be responsible for the development of rectal cancer. Thus, a detailed history, digital rectal examination and rectosigmoidoscopic examination are important, particularly in patients with long-term rectal prolapse.