BACKGROUND Long-term results of conservative treatment of acute locked posterior shoulder dislocation with a reverse Hill-Sachs defect (Malgaigne lesion) <25% are rare. The aim of the present study was to evaluate the clinical and radiological results of patients after conservative treatment. METHODS In this study 8 patients (8 male, average age 58.4 years) after non-operative treatment consisting of closed reduction and immobilization in 15° of external rotation were retrospectively clinically and radiologically examined (true anteroposterior, axillary and y view) The Constant score (CS), Rowe score (RS), Western Ontario shoulder instability index (WOSI) and the subjective shoulder value (SSV) were evaluated. RESULTS After a mean follow-up of 5.4 years (range 5-7 years) no patient reported a redislocation or resubluxation or a persistent feeling of instability. None of the patients stated that they had to avoid certain movements or were limited in their everyday life. The clinical tests for posterior instability (jerk test/Kim test) were negative in all patients. The mean CS was 87.4 (range 42-98) points, the RS 96.4 (range 55-100) points, the WOSI 89.1% (range 41-100%) and the SSV 89.1% (range 50-98%). The radiological evaluation of the affected shoulder in true anteroposterior, axillary and y views showed signs of osteoarthritis (grade II according to Samilson and Prieto) in two cases. The humeral head was centered in all eight cases. CONCLUSIONS Non-operative treatment of acute locked posterior shoulder dislocation demonstrated good to excellent clinical and radiological long-term results in this study. It represents the treatment of choice in patients with a reverse Hill-Sachs defect (Malgaigne lesion) < 25% and a duration of dislocation < 3 weeks.