The shape of the mesopores in a series of Y zeolites modified with different postsynthesis treatments was investigated. A combination of 3D-TEM (3D-TEM = three-dimensional transmission electron microscopy) with texture analysis (nitrogen physisorption and mercury porosimetry) enabled us to discriminate between cylindrical mesopores and mesoporous cavities inside the zeolite that are connected to the external surface via micropores. A large part of the mesopores in steamed and acid leached zeolite Y proved to be cavities, although the cylindrical mesopores in these samples account for the majority of the mesopore volume. Only after special hydrothermal treatments a zeolite Y with almost exclusively interconnected cylindrical mesopores is obtained.