A needle insertion and retraction mechanism for a drug delivery device, comprises a motion source, a user-operated control for the motion source, an interrupter for stopping motion of the motion source at a predetermined location and thereby dividing the motion into two parts which are continuous relative to each other. A motion translation mechanism connects the source of continuous motion to a needle, to extend the needle during the first motion part and to retract the needle during the second motion part. The needle is thus extended and retracted by continued operation of a single tension source rather than two tension sources operating in opposition to each other. The motion source may be a spring, and a winding mechanism may be provided to wind the spring. The second motion part may be initiated by pulling the adhered delivery device from the skin.
