Here, we report 12 cases of anorectal malignant melanoma (ARMM), which has a very rare incidence. Patients were examined by either computed tomography or MRI or computed tomography combined with MRI before they underwent a remission operation. Because of the paramagnetic contribution from melanin, the short T1 and short T2 signals in MRI were specific to melanoma. MRI is reliable in the early diagnosis of ARMM, which is confirmed by pathological reports. Therefore, we advocate the application of a radiological screen using MRI for those patients with a mole in the anorectal region and abnormal colonoscopy findings.