BACKGROUND Capsule endoscopy has played a significant role in small bowel investigation, providing the opportunity of detecting neoplastic lesions to a greater degree and at an earlier stage than other diagnostic procedures. Failure to excrete the capsule with the feces within 48 h can lead to capsule retention with increased risk of further complications such as bowel obstruction and perforation. Capsule retention can remain undetected in case of incomplete follow-up and poor patient compliance. Acute small bowel obstruction as late as many months following capsule endoscopy investigation is very rare, with only a few cases reported in the published literature. We herein report a rare case of prolonged capsule retention which remained undiagnosed, resulting in small bowel obstruction 6 months after the initial investigation. CASE REPORT An 82-year-old woman presented with abdominal pain and symptoms suggestive of intestinal obstruction. The patient history included a capsule endoscopy investigation because of episodes of abdominal pain 6 months prior to admission. Both the outcome of the investigation and the excretion of the capsule remained undetermined due to her history of dementia and follow-up failure. Radiologic investigations identified the capsule causing small bowel obstruction. Upon surgery, the capsule was found to be impacted in a stenotic small bowel lesion, and a segmental small bowel resection was performed. Histologic examination revealed the presence of a stenotic small bowel neuroendocrine tumor. CONCLUSIONS Appropriate follow-up is necessary to diagnose the complication of capsule retention which, if it remains unrecognized, can cause life-threatening complications as late as many months after capsule endoscopy.