Aim. We present the greatest study of patients with proximal fibula resection. Moreover we describe a new classification system for tumour resection of the proximal fibula independent of the tumour dignity. Method. In 57 patients the functional and clinical outcome was evaluated. The follow up ranged between 6 months and 22.2 years (median 7.2 years). Indicationfor surgery was in 10 cases benign tumours and in 47 cases malignant tumours. In 32 patients a resection of the peroneal with resulting peroneal palsy was necessary. Results. In 13 of 45 patients, where a resection of the lateral ligament complex was done, knee instability occurred. Patients with peroneal resection had a significant worse functional outcome than patients without peroneal resection. An ankle foot orthosis was tolerated well by these patients. 3 of 4 patients with pathologic tibia fracture had a local radiation therapy. There was no higher risk of tibia fracture in patients with partial tibia resection. There was a significant better outcome of patients with benign than of patients with malignant tumours. Conclusion. Resection of tumours in the proximal fibula can cause knee instability, peroneal palsy and in case of local radiation therapy a higher risk of delayed wound healing and fracture. Despite the risks of proximal fibula resection good functional results can be achieved