BACKGROUND Infectious abscesses in the abdominal wall can be secondary to retained foreign bodies (e.g., stones, use of artificial mesh, use of silk yarn in surgical suture), inflammatory diseases (e.g., acute appendicitis), and perforated malignancies of the digestive tract (particularly the colon). Aseptic abscesses (AAs) are relatively rare. To the best of our knowledge, this is the first report of an AA in the abdominal wall accompanied by monoclonal gammopathy of undetermined significance (MGUS) at 5 years after laparoscopic proctectomy. CASE SUMMARY A 72-year-old female patient presented with an enlarged painless mass in the lower abdomen for 1 year. She had a history of obesity, diabetes, and MGUS. Her surgical history was laparoscopic resection for rectal cancer 6 years prior, followed by chemotherapy. She was afebrile. Abdominal examination revealed a smooth abdomen with a clinically palpable solid mass under a laparotomy scar in the left lower quadrant. No obvious tenderness or skin redness was spotted. Laboratory data were not remarkable. Computed tomography scan revealed a low-density mass of 4.8 cm in diameter in the lower abdominal wall, which showed high uptake on positron emission tomography. The preoperative diagnosis was an abscess or tumor, and surgical resection was recommended. The mass was confirmed to be an AA by microbiological and pathological examinations. The patient recovered well after surgery. There was no evidence of recurrence 2 years later. CONCLUSION It is important to consider underlying conditions (diabetes, chemotherapy, MGUS) which may contribute to AA formation in the surgical wound.