Objectives: This study assesses the anatomical outcome of subfascial endoscopic perforator vein surgery (SEPS) in cases where no perioperative marking of incompetent perforators was used. Methods: Patients who had undergone SEPS and who had been investigated with a preoperative duplex ultrasound scan were identified from hospital records. These patients were recalled for a follow-up duplex ultrasound scan, which was compared with the preoperative investigation. Results: In total, 15 patients (17 limbs) were studied. Four legs (23.5%) had no incompetent perforators at follow-up scan. The remaining 11 limbs (76.8%) all had at least one incompetent perforator. Six limbs (35.2%) showed incompetent perforators in the same position as the incompetent perforators identified at the preoperative duplex scan. A total of 10 incompetent perforators persisted at follow-up (35.7% of preoperatively identified incompetent perforating veins). Nine legs (52.9%) had developed at least one new incompetent perforator since undergoing SEPS. Conclusion: In our study, a large proportion of incompetent perforators persisted at postoperative follow-up duplex scan. These probably represent perforators missed during surgery. Endoscopy of the subfascial space alone is not a reliable method for incompetent perforator identification. Alternative methods of localization should be employed perioperatively.