Foreign body ingestion is a common presentation in the emergency room. However, the complication such as penetrating renal trauma due to sharp objects ingestion is relatively rare. We herein describe an unusual case of penetrating renal trauma in the absence of any other urinary symptoms. A 53-year-old man who had a history of iron wire ingestion went to our hospital, on examination, he only had slight abdominal tenderness due to swallowing a ball pen and 1 cap nut 1 day before, radiological imaging showed penetrating renal trauma, the blood test showed his renal function is normal. Surgical strategies were recommended to remove the pen and the iron wire simultaneously, nonetheless the patient eventually agreed to only receive surgical removal of the swallowed ball pen and cap nut, meanwhile leave the kidney untreated. During 30 months follow-up by phone and regular outpatient examination, he recovered unevenly and had no special complaint. Such cases remind us that chronic penetrating renal trauma due to foreign object ingestion may have no obvious symptoms. It is easily to be neglected. We should try to minimize the possibility of missed lesions by adhering to a meticulous examination technique.