Classification systems for fractures of the femur with a prosthetic hip in situ are diverse and complex. Most of them are based on the site of the fracture, which is not the most important differentiating factor in treatment planning. The Coventry classification system groups the periprosthetic fractures into 'happy hips' and 'unhappy hips' based on whether or not the stem is loose. In 'happy' hips, treatment only needs to address the fracture itself, unless the fixation has been compromised by the fracture. In the 'unhappy hips', revision of the prosthesis is recommended.