Abstract: The present disclosure relates to a medicament delivery device comprising: a reservoir for medicament; a dispensing mechanism operable to dispense medicament from the reservoir, the dispensing mechanism comprising a sleeve configured to rotate during the dispensing of medicament and having a plurality of formations at an end of the sleeve; and a dosage measurement system comprising at least one mechanically actuated sensor configured such that, in use, rotation of the sleeve causes successive formations to engage the sensor such that the sensor detects rotation of the sleeve and a processor configured to determine a dosage dispensed from the medicament reservoir based on the detected rotation of the sleeve.