An adjustable spa headrest has two side surfaces laterally disposed between front and back surfaces. A first projection extends outwardly from one of the side surfaces. A guide rail, positioned for receiving the projection, allows the spa headrest to be positioned in a number of positions. The guide rail includes a horizontal slot, a vertical slot including a number of spaced notches, each notch defined by a pair of second projections, and a spring arm depending in the vertical slot. When the first projection moves to a position between one of the second projections and the spring arm, the spring arm moves away from the second projection whereupon the spring arm applies a spring force to the first projection in a direction of second projection. In response to positioning the first projection in one of the notches, the spring arm secures the first projection in the one of the notches.
