Abstract: A ladder or ladder-like structure comprising at least one elongated, hollow extruded rail member of uniform cross-section throughout its length with at least one continuous longitudinally extending groove formed inwardly from the outer surface. The groove extends into the rail member and has an outer width which is narrower than its inner width. The rung members of the ladder are connected to the rail member by connector members which include a first portion having a shape generally corresponding to the shape of the groove and slidable longitudinally in the groove. To maintain a desired spacing between adjacent rung members, slidable spacer members are received in the groove and have a cross-sectional shape corresponding to the groove shape. Also, means are provided for preventing the spacer members and the connector members from sliding out of the groove.