BACKGROUND Sigmoid colon adenocarcinoma has a high incidence among gastrointestinal tumors, and it very rarely metastasizes to the penis. The literature reports that the prognosis after penile metastasis is generally poor, with a median survival of about 9 mo. Metachronous isolated metastasis to the penis originating from sigmoid colon adenocarcinoma has not been reported so far. Here, we report a case of sigmoid colon adenocarcinoma with isolated penile metastasis occurring 2 years after surgery. The mass was pathologically confirmed as metastatic adenocarcinoma, and oral chemotherapy with capecitabine was given after surgery. The tumor did not recur during the 2-year follow-up period. CASE SUMMARY A 79-year-old man presented to the urology department with "a mass located at the root of the penis since 1 mo". Enhanced computed tomography (CT) examination suggested a 12 mm × 10 mm × 9 mm nodule at the root of the right penile corpus cavernosum. Cranial, pulmonary, and abdominal CT; and bone scan did not show any tumorigenic lesions. The carcinoembryonic antigen (CEA) level was slightly elevated (6.01 ng/mL, reference value 0-5 ng/mL). The patient had undergone laparoscopic radical sigmoidectomy for sigmoid colon cancer 2 years ago. The postoperative pathology showed moderately differentiated adenocarcinoma of the sigmoid colon, and the stage was PT2N0M0. The penile mass was removed under general anesthesia. The postoperative pathology showed adenocarcinoma, and immunohistochemistry showed CDX2(+), CK20(+), and Villin(+). Based on the medical history, he was diagnosed with penile metastasis from sigmoid colon adenocarcinoma. The CEA level returned to normal (3.34 ng/mL) 4 d after surgery. Oral chemotherapy with capecitabine was given subsequently, and tumor recurrence was not found during the 2-year follow-up period. CONCLUSION To our knowledge, this is a rare case of metachronous isolated penile metastasis from sigmoid colon adenocarcinoma. The penis is a potential site of metastasis of colon adenocarcinoma, and the possibility of metastasis should be considered in patients with a history of colon cancer who present with a penile mass. Solitary penile metastasis can be removed surgically, in combination with chemotherapy, and it may have good long-term outcomes.