Abstract: An expandable file folder made from a substantially unitary blank of relatively stiff sheet plastic and having a front panel, a rear panel, a rectangular bottom wall connected along opposite marginal edges to the front and rear panels along fold lines, and end walls connected to opposite transverse edges of a selected one of the front and rear panels and having their free edges connected to connecting tabs formed on the other of the front and rear panels. A tucking flap is hingedly connected to a lower transverse edge of each of the end walls and is positionable to overlie the bottom wall so as to provide additional supporting strength for the bottom wall. The bottom and end walls preferably have fold lines along their longitudinal centerlines which enable lateral expansion and compressing of the file folder.