The present invention is generally directed to a drug delivery device for selecting and dispensing a number of user variable doses of a medicament. The device comprises a housing (10) and at least two separate component parts (40; 60), wherein for example at least one of these component parts (60) performs a movement relative to the housing (10) during dose setting and for example at least one of these component parts (40; 60) performs a movement relative to the housing (10) during dose dispensing, and wherein the relative movement of the at least two separate component parts (40; 60) with respect to each other during dose setting differs from the relative movement of the at least two separate component parts (40; 60) with respect to each other during dose dispensing. The device further comprises a monitoring device (130), wherein at least one component part (70; 120) of the device is diaphanous to allow optical detection of the movements of the at least two separate component parts (40; 60) relative to the housing (10), relative to the monitoring device (130) and/or relative to each other during dose setting and/or during dose dispensing by the monitoring device (130).