Reconstructive surgery of the anterior cruciate ligament (ACL) of the knee in young active patients is a routine procedure, but with certain risks that need to be taken into account. Peroperative patellar fracture after bone-patellar tendon-bone autograft harvesting is a rare complication, which can significantly impair the functional outcome of ACL single-bundle reconstruction. We report the case of a patient presenting with disabling patellofemoral syndrome 3 years after arthroscopic ACL reconstruction by bone-tendon-bone autograft, revealing unnoticed mal-union of a iatrogenic sagittal patellar fracture. Patellar osteotomy corrected this painful iatrogenic patellar instability.