Abstract: Weathertight fitting (41) for the mounting of the tail vertical stabilizer of an aircraft in a rear area of its fuselage, the construction being based on a casing (5) made with a composite material as one unitary piece and some frames (7) that are comprised of: one first piece (43) comprised of two bodies (45, 45?), that include the mounting lugs (47, 47?) for the tail vertical stabilizer and some vertical walls (49, 49?) for joining the fitting (43) to the frames (7) of the fuselage, and a weathertight central profile (51); two pairs of additional pieces (55, 55?; 65, 65?) of angular shape, that include some horizontal walls (57, 57?; 67, 67?) for joining to the casing (5) and some vertical walls (59, 59?; 69, 69?) for joining to the aforementioned bodies (45, 45?). All the weathertight fitting's (41) pieces are made with a composite material.