In young patients referred for exercise-induced pain in the legs, false positive tests are a potential problem for the post-exercise ankle–brachial index (ABI) test when using the current American Heart Association guidelines for diagnosing peripheral artery disease (PAD). The present study aimed to investigate post-exercise ABI in healthy young people, and to explore whether the current diagnostic criteria for pathological ABI should be revised. Forty-eight volunteers (18–30 years) were included. Resting examinations included ABI and ultrasound of the external iliac artery. Post-exercise examinations after a treadmill load included ABI and ultrasound of the external iliac artery; after 0 min and after 3 min. A total of 60.5% of the participants had a post-exercise decrease in ABI > 20%. A total of 6.5% showed a decrease in ankle systolic blood pressure >30 mmHg. No significant association was observed between a change in blood flow in the external iliac artery and a reduction in ABI post-exercise. Analyses of the ultrasound recordings showed no turbulence in the external iliac artery. According to the results, a 20% decrease in ABI post-exercise seems to be a physiological condition present in young people. We support the need for a reassessment of the criteria for diagnosing PAD.