An auto injector assembly comprises a medicament container defining a substantially cylindrical chamber containing a liquid medicament. A proximal end of the chamber is closed by a piston and a distal end of the chamber is closed by a seal spanning an opening. A biasing means such as a spring is coupled to the piston and acts to bias the piston towards the seal thereby pressurising the liquid medicament. The assembly also comprises a hypodermic needle and a removable needle cap for maintaining the hypodermic needle in sterile conditions until use. A means for establishes fluid communication between the chamber and the hypodermic needle such that the pressurised liquid medicament is automatically delivered through the hypodermic needle when communication has been established.
