Abstract: An adjustable staircase assembly comprises a pair of channel section stringer members having spaced tread support pivots adjacent their lower edges and tread locating apertures adjacent their upper edges, the tread locating apertures being spaced along arcs each having its origin at the tread support pivot axis. After the stringers are attached to a structure, the tread supports are pivoted to a horizontal position and a tab on each tread support is located in a suitable locating aperture in the sloping stringer such that the tread support is horizontal.