PURPOSE: Rectal or anal canal adenocarcinoma with inguinal lymph node metastasis (ILNM) is rare and is associated with poor prognostic outcomes. This study aimed to elucidate the clinical significance of neoadjuvant therapy followed by selective inguinal lymph node dissection and total mesorectal excision for rectal or anal canal adenocarcinoma with clinically suspected ILNM. METHODS: This study enrolled 15 consecutive patients who underwent neoadjuvant therapy and curative resection for rectal or anal canal adenocarcinoma with clinically suspected ILNM between 2005 and 2019 at a single institution. Inguinal lymph node dissection was selectively performed on the side of suspected metastasis before neoadjuvant therapy. Short- and long-term outcomes were retrospectively reviewed. RESULTS: Out of the15 patients, 11 were treated with neoadjuvant chemoradiation, three with chemotherapy, and one with chemoradiation followed by chemotherapy. Fluorodeoxyglucose (FDG)-positron emission tomography (PET) scans were performed after neoadjuvant therapy in 14 patients. Five patients had negative FDG accumulation in inguinal lymph nodes on FDG-PET scan, and their inguinal lymph nodes were also pathologically negative for metastasis. Of the nine patients who had positive FDG accumulation, four had pathologically positive inguinal lymph nodes. Seven patients (46.7%) had inguinal seroma postoperatively. Five-year-overall survival was 77.5%, and 5-year-relapse-free survival was 64.2%. No patient had a recurrence in the inguinal region. CONCLUSION: In patients with rectal or anal canal adenocarcinoma associated with clinical ILNM, radical resection with neoadjuvant therapy provides a good long-term survival.