Abstract: A closed-riser, adjustable rise, staircase system is provided which allows a plurality of stair treads to be assembled into staircases having different rise heights, for example, from six inches to seven inches, while maintaining the closed-riser nature of the staircase. The nose piece portion extending downwardly from the walking surface of each stair tread is dimensioned such that the distance to which it extends is greater than the desired range of adjustability of rise heights, and the riser portion of each stair tread is dimensioned such that, when positioned for the maximum desired rise height, an upper portion of the riser will continue to extend behind the nose piece of the stair tread positioned immediately above.