Abstract: A hinge is disclosed for folding doors appropriate for use in lavatories on airplanes where the highest degree of airtightness is required. It consists of a basic frame hollow in shape, and a pair of moving frames. The moving frames have longitudinal flanges to support the door panel and connect with the opening slit of the basic frame by way of the supporting pieces. Longitudinal cogs are provided on the end of the supporting piece, such that they engage one another to rotate and enable smooth operation of the hinge. Each cog has a semicircular interior surface which cooperates with supporting shafts of the basic frame for rotation therearound.