Abstract: A sound for uterine measurement including an elongated probe provided with expandable wings at one end. A button may be selectively moved to control the extension or collapse of the wings and a stop is reciprocally mounted on the probe and has a stop surface facing the wings which is adapted to engage the cervix. A coil spring surrounds the probe and biases the stop toward the distal end of the sound and a measuring scale is carried by the instrument. A moveable index point is provided and connected to the stop so as to cooperate with the scale depending upon relative positioning of the stop on the probe. A protective housing surrounds the spring for all positions of movement of the stop to prevent the spring from coming in contact with the tissue of a patient. Preferably, the protective housing is transparent and carries the scale with the index being movable within the housing.