BACKGROUND Direct fixation of the posterior malleolus through a posterolateral approach is increasing in popularity. However, data is limited, and no studies have stratified results by posterior malleolus size. METHODS A retrospective cohort study of patients with posterior malleolus (PM) fractures undergoing internal fixation over an 18-month period was conducted. Radiographic and patient reported outcomes measures (PROMs) were assessed. 75 patients were included, and 31 returned Manchester-Oxford Foot and Ankle (MOXFQ), EQ-5D-3 L, 5-point Likert satisfaction questionnaires. Mean age was 56.2 years, 68% were female, mean ASA was 1.72, 6.7% were diabetic, and average surgical time was 75.7 min (±40.9). RESULTS Overall, the MOXFQ summary score was 26.9 (±25.8), with the pain domain showing the most severe score 32.4 (±24.0). The EQ-5D VAS index was 0.75 (±0.24). Larger PM size was associated with more anatomical reduction (58.8%, n = 20 of <10% vs. 90.9%, n = 10 of >30%) and larger sized fragments were more likely to be fixed posteriorly. Best PROMs were observed in PM fragments <10%, and the worst in fragments 10-20%. A tendency towards more secondary surgery was observed with posterior subluxation 21.9% (n = 7) vs. 7.0% (n = 3) (p = 0.06). CONCLUSIONS Patients with fragments >10% have an intra-articular injury. We recommend direct anatomic reduction and rigid internal fixation. METHODS Level III, retrospective comparative study.