The invention relates to an elevator comprising an elevator car unit containing at least two elevator cars and to a procedure for controlling the elevator. According to the invention, at least one elevator car can be moved vertically within the elevator car unit relative to its frame. The procedure is characterized in that prior to start-up, the exact distances between landings are measured and stored in memory. The distance data corresponding to the control instruction according to a unit call or car call is then determined, and based on this data, the elevator car unit is caused to move in the shaft to a position corresponding to the call. At least one of the elevator cars is caused to move relative to the frame of the unit to a position corresponding to the distance between the floors in question.