Introduction: Surgical treatment of tumors of the head and neck region is associated with extensive tissue defects. The introduction of modern reconstructive surgery techniques allows replace the resected bone and soft tissue. The aim of reconstruction is to fill the defect and ensure proper appearance and functioning of affected area, but functional defects caused by harvesting the graft are also important for the patient. The aim of this paper is to describe changes in gait pattern and gait parameters after harvesting free fibular flap and the flap from the iliac crest for reconstruction of the mandible in patients treated for head and neck cancer. Material and methods: Two patients who underwent reconstruction with fibular and iliac crest flaps had gait tests performed three times: before, one month and three months after surgery. The patients had an intensive rehabilitation and physiotherapy started on 1st postoperative day and it was continued for 2 months. Results: The analysis of tests results showed deterioration in gait parameters one month after operation. 3 months after operation these parameters returned to the level before surgery. Conclusions: Harvesting fragment of fibula and of iliac crest affects the function of gait. Systematic physical therapy and rehabilitation on inpatient and outpatient basis allowed the patients to return to the same level of gait functioning as before the operation. Further research is needed to develop a more complete picture of patobiomechanic after bone resection. The results will help to create standard procedure after both treatments.