OBJECTIVE This article introduces a simple and reproducible classification of the degree of atrophy in fractures of the atrophic edentulous mandible, and evaluates the results of treatment in 84 consecutive fractures based on this classification. METHODS Eight-four fractures of the edentulous mandible, with a height at the fracture site of < or = 20 mm, were included. Using the ratio of actual plate width to plate width on the postoperative radiograph, the actual height of the mandible at the fracture site was calculated. Twenty-five fractures (30%) were in the Class I atrophy group (height at the fracture site 16 to 20 mm), 33 fractures (39%) occurred in Class II atrophic mandibles (height 11 to 15 mm), and 26 fractures (31%) were seen in extremely atrophic Class III mandibles (height < or = 10 mm). The treatment was performed by compression plating without any postoperative MMF. Primary bone grafting was used in six cases (7%) because a partial bone defect was present at the fracture site. RESULTS In 81 (96.5%) of the 84 fractures an uncomplicated, solid, bony union was achieved. Three major complications occurred: one osteomyelitis and two nonunions. The two nonunions occurred in bilateral fracture of an extremely atrophied mandible (Class III atrophy). Minor soft tissue infections, without interference with fracture healing, were observed in six cases (7%). CONCLUSIONS Because there is an obvious relation between the height of the mandible and the incidence of complications in fracture healing, a special classification of the degree of atrophy is needed. In fractures of the extremely atrophic mandible (Class III atrophy) periosteal degloving should be avoided and supraperiosteal placement of plates is recommended. Compression osteosynthesis has proved to be a successful method, with minimal impairment of the patient and a low frequency of serious complications.