RATIONALE: Early rectal cancer is mostly confined to the mucosa or submucosa, and metastasis to lymph nodes is rare. Stage 0 rectal cancer can usually be cured by endoscopic resection. However, when patients present with enlarged lateral lymph nodes of uncertain nature, additional surgical intervention should be considered. This article reports a case of early rectal cancer combined with ulcerative colitis. Preoperative imaging examination revealed enlarged right-sided group 263D lymph nodes. Since the nature of the enlarged lymph nodes cannot be determined, it was decided to perform lateral lymph node dissection combined with endoscopic submucosal dissection to achieve clear diagnosis and treatment. This article aims to illustrate the importance of individualized treatment for patients with early rectal cancer with complex clinical backgrounds and the clinical value of lateral lymph node dissection combined with endoscopic submucosal dissection. PATIENT CONCERNS: The patient was a 66-year-old male who presented with blood in the stool for 1 month with no family history of hereditary tumors. DIAGNOSIS: Colonoscopy and further biopsy diagnosed early rectal malignancy (stage 0). Pelvic magnetic resonance and enhanced computed tomography showed enlarged right group 263D lymph nodes with well-defined borders, approximately 1.2 cm in diameter. Together with the patient's history, the possibility of metastasis of rectal cancer was considered, but the lymph nodes were diagnosed as reactive hyperplasia after lateral lymph node dissection. INTERVENTIONS: Since the nature of the enlarged lymph nodes could not be determined, it was decided to first perform lateral lymph node dissection to rule out the possibility of metastasis, followed by endoscopic submucosal dissection to remove the tumor. OUTCOMES: The patient recovered well after surgery. Pathological examination showed reactive hyperplasia of the lymph nodes, and the tumor was completely resected with negative margins. LESSONS: Lymph node metastases rarely occur in early rectal cancer, but this possibility should not be ignored, especially when dealing with patients with complex clinical backgrounds. This case also emphasizes the importance of individualized diagnosis as well as the extremely high clinical value of Lateral lymph node dissection combined with endoscopic submucosal dissection, and provides a reference for the diagnosis and treatment of similar cases.