The present invention relates to an automatic injector having a drive assembly with an actuator extending from the rearward end portion of the housing and a removal resistant cover for preventing unintended operation of the actuator. The present invention also relates to a sealing arrangement wherein the needle is sealed within a sterilized needle chamber by at least three sealing members which cooperate to form the chamber. Also, the present invention relates to an injector in which the cartridge is mounted to a tubular cartridge mounting portion of the needle carrier with an annular sealing member disposed therebetween. The cartridge mounting portion has at least one generally axially extending groove which allows air to escape from the cartridge mounting portion as the cartridge is being moved forwardly to a medicament supplying position.