Background The purpose of this study was to assess low molecular weight heparin auto-injection skills of self-supporting patients, taught by a nurse through a rapid demonstration in an emergency department. Methods The study was a prospective, multicentre study, carried out in emergency departments. It included all ambulatory attending patients over 18 years of age, who were given a lower limb cast in an emergency ward and provided with limited orthopaedic treatment. Eligible patients who accepted self-injection training were given a quick demonstration by the nurse in the emergency ward. A questionnaire about the perception of the patient was completed at the beginning of the treatment and at the end of the treatment. A surveillance chart for recording injections and side effects was also given to the patient, and platelet counts were performed twice weekly. Findings Two hundred and fourteen patients have been assessed. Forty-four patients (20.5%) were judged inappropriate for training (n=19) or refused it (n=25). Primary perception of the self-injection method showed absence of fear of injections among patients in 43.7% of cases. Training was successful in 88% of cases. Twenty-one patients out of 170 (12%) gave up after completing the training. Questionnaires given at the end of the treatment found a generally favourable opinion on self-injections among 73.26% of patients (n=86). Compliance was good – 95.5% of patients completed all their injections. Platelet counts were considered appropriate only in 52.5% of cases. Interpretation It seems possible to extend the practice of self-injection to other types of injections prescribed after discharge from the emergency department, such as preventive low molecular weight heparin for surgical or medical purposes and curative ambulatory low molecular weight heparin treatment for deep vein thrombosis.