Here, we report our experience with a 5-mm trocar site hernia (TSH) near a stoma. This is the first report describing the relationship between TSH and extraperitoneal colostomy. A 72-year-old man underwent laparoscopic abdominoperineal resection with extraperitoneal sigmoid colostomy and partial hepatectomy for rectal cancer accompanied by synchronous liver metastasis (pT3N1aM1a Stage IVA Union for International Cancer Control [UICC] 8th edition). The surgical procedures were completely performed without morbidity. After 1 year, he presented to our hospital with sudden nausea. Computed tomography (CT) revealed small bowel obstruction due to a 5-mm TSH, 1 cm from the stoma. The patient underwent laparoscopic hernia repair. The incidence of a 5-mm TSH is low. However, an abdominal wall vulnerability caused by the extensive exfoliation of the retroperitoneum due to the construction of the colostomy was observed, and the extraperitoneal colostomy influenced the onset of the 5-mm TSH. When the port and hernia sites are located in close proximity to each other, even a 5-mm trocar site may increase the incidence of TSH.