Due to the increasing life expectancy, orthopaedic surgeons are more and more often confronted with fragility fractures of the pelvis (FFPs). These kinds of fractures are the result of a low-energy impact or they may even occur spontaneously in patients with severe osteoporosis. Due to some distinct differences, the established classifications for pelvic ring lesions in younger adults do not fully reflect the clinical and morphological criteria of FFPs. Most FFPs are minimally displaced and do not require surgical therapy. However, in some patients, an insidious progress of bone damage leads to increasing displacement, nonunion and persisting instability. Therefore, new concepts for surgical treatment have to be developed to address the functional needs of the elderly patients. Based on an analysis of 245 consecutive patients with FFPs, we propose a novel classification system for this condition. This classification is based on morphological criteria and it corresponds with the degree of instability. Also in the elderly, these criteria are the most important for the decision on the type of treatment as well as type and extent of surgery. The estimation of the degree of instability is based on radiological and clinical findings. The classification gives also hints for treatment strategies, which may vary between minimally invasive techniques and complex surgical reconstructions.