Pertrochanteric hip fractures still are a major orthopaedic challenge, and those that are unstable have the poorest prognosis. Fracture collapse is one of the postoperative complications reported in association with these fractures. My objective was to evaluate possible causes for pertrochanteric hip fracture collapse. Twenty-four patients with documented postoperative fracture collapse were evaluated retrospectively. The findings showed unequivocally that in all patients, this complication followed fracture of the lateral wall and resulted in protracted period of disability until fracture healing. The importance of the integrity of the lateral wall for event-free fracture healing clearly is indicated, and fracture of the lateral wall should be avoided in any fixation procedure. The presence of the lateral wall on the preoperative radiograph should be a major factor in determining the internal fixation device used for fracture stabilization. In unstable pertrochanteric hip fractures, the traditional description of the posteromedial fracture part as the most important prognostic factor should be revised to include the structural description of the lateral wall. Special caution should be taken when drilling at the base of this often delicate structure.