Abstract: An operatory stool having an arcuate, body support arm positioned above the level of the stool seat is described. The body support arm is reversible for right- or left-handed use of the stool. The stool structure permits rapid interchange between the right- and the left-handed configurations by means of a rotatable mechanism between the body support arm and a connecting member between the body support arm and the seat, which permits rotation of the body support arm through a 180.degree. upwardly extending arc from one side of the connecting member to the other. Means are provided for locking the body support arm at dependent positions on either side of the connecting member. Additionally, a reversible locking mechanism for resisting rotation of the body support arm about the connecting member in a predetermined direction in a horizontal plane is provided.