Cartons of the leakproof type comprising a rectangular sleeve each end of which is formed with crease lines to present four closure wall portions or flaps, two of said flaps being further provided with crease lines defining triangular portions to provide gussets, are closed by apparatus comprising means for holding a carton in position for closure, a pair of angularly movable pressure plates adapted to engage the triangular portions of the end wall flaps and to partially fold inwardly the end and side wall flaps, a pair of spaced pressure rods to further fold inwardly the end and side wall flaps so that the free ends of the side wall flaps are in overlapping engagement, and a pressure bar provided to engage the overlapping side wall flaps along a previously applied line of adhesive. A reaction plate may be provided to co-act with the pressure bar. The end closure apparatus may be incorporated in an installation for filling and closing cartons.