A medicament delivery device comprises a housing and a syringe axially movable in the housing and the syringe having a barrel. The device further comprises a stopper axially movable in the barrel and which separates a first chamber and second chamber from one another. The stopper is axially movable in the barrel in response to a vapour pressure being received in the second chamber. The device also includes a biasing mechanism to axially move the syringe in the housing between a first syringe position and a second syringe position in response to a first reduction in the vapour pressure in the second chamber. In the first syringe position venting of the propellant from the second chamber through a first fluid pathway is permitted to enable the first reduction in the vapour pressure in the second chamber while venting of the propellant from the second chamber through a second fluid pathway is substantially prevented. In the second syringe position venting of the propellant from the second chamber through the second fluid pathway is permitted to enable a second reduction in the vapour pressure in the second chamber.