Abstract: A plastic ceiling panel is mounted in a grid of T-rails. The ceiling panel is shaped complementarily to the space defined by facing edges of the T-rails, and includes a central web and sidewalls extending upwardly from the central web. The sidewalls include a lower part that projects halfway across a lower surface of the T-rail, to butt against the corresponding lower part of contiguous panels in spaces surrounding the first panel, so as to give the impression of a continuous, uninterrupted ceiling. The sidewalls are stiffly flexible and are provided with a channel into which the facing edge of each of the T-rails forming the grid space in which the ceiling panel is seated, is received.