The present invention relates to a medicament injection apparatus, particularly suitable for use by those with diabetes in which, in use, once a desired dosage of medicament has been selected and expelled from the medicament cartridge into the body of the patient, the injected medicament is allowed to disperse locally from the injection site within the patient's body before the needle arrangement is removed from the patient's body. It is considered to be a problem that in known medicament injection devices the injection interval, that is the time elapsed since a previous injection, is measured following completion of a delivery stroke rather than from dispersion of the injected medicament. A medicament injection device is disclosed in which the time elapsed following an injection operation is calculated from the end of a predetermined period during which medicament is permitted to disperse subsequent to completion of an injection stroke.