Background: The deep circumflex iliac artery (DCIA) free flap is a well-established option for mandibular and maxillary reconstruction, offering favorable bone height, contour, and potential for dental rehabilitation. However, donor-site morbidity remains a limitation, with anterior superior iliac spine (ASIS) fracture representing a rare but clinically relevant complication. Methods: We report two cases of ASIS fracture following DCIA flap harvest and analyze underlying mechanisms and preventive surgical considerations. Clinical presentation, imaging findings, operative details, and outcomes were reviewed. Results: A 33-year-old male with mandibular ameloblastoma and a 77-year-old male with osteoradionecrosis underwent segmental mandibulectomy with DCIA free flap reconstruction. Both patients developed postoperative hip pain and gait disturbance. CT imaging confirmed Type A ASIS fractures. Surgical planning analysis demonstrated that bone harvesting was performed close to the ASIS, leaving residual bone bridges of 16.1 mm and 20.6 mm. Both patients were managed conservatively with physiotherapy and activity modification, achieving good functional recovery. Discussion: ASIS fractures are likely due to weakening of the anterior iliac crest combined with traction forces from the sartorius and tensor fascia latae muscles during early mobilization. Biomechanical studies indicate that harvesting within 20–25 mm of the ASIS significantly reduces iliac crest strength, whereas preserving a ≥2–3 cm bone bridge improves structural integrity. Conclusion: ASIS fracture is an uncommon but important complication following DCIA flap harvest. Early recognition of donor-site pain is essential. While conservative management is often sufficient, prevention remains key. Maintaining an adequate distance from the ASIS and careful surgical technique can significantly reduce fracture risk.