Abstract: A stringer module for a self-supporting modular stairway in which each riser is composed of two modules (A), each module being manufactured from sheet metal, each module having an L-shape defining a base portion and a riser portion located at a first side of the base portion, whereby an overlap of the riser portion with an opposed part of the base portion of an adjacent like module defines a vertical riser of said stairway and the remaining base portion its tread. The riser portion is located above the base portion, the plane of the riser portion is folded to be offset relative to the base portion such that the base portions of adjacent modules are coplanar when overlapped. The overlapping portions of each module are provided with a series of horizontal slots on one portion and corresponding series of holes on the other portion, adjacent modules being secured in overlapping position by means of retractable pin-keys (B) engaging the holes and slots.