Rectosigmoid mucinous adenocarcinoma that is Synchronous with an anal fistula is a very rare condition thus its diagnosis and management are challenging. Here, we showed the diagnosis and management of a single case for a 57-year-old Saudi male presented with low rectal mass and gluteal abscess and a history of recurrent perianal abscesses that was managed as benign tumor and without a family history of neoplasms of re colorectal parts. After reviewing the literature concerning the aetiopathogenesis of this case and the suggested treatment. The clinical examination showed a perianal fistula and a digital rectal examination was conducted after incision and drainage of the right gluteal abscess then rigid sigmoidoscopy was performed and biopsy was collected showing invasive moderately differentiated adenocarcinoma. The decision was to avoid radiation preoperative due to abscess and extensive perianal disease and a treatment plan was initiated and the patient was followed up with regular CT examination.