Direct laser writing based on two-photon absorption allows the fabrication of almost arbitrary three-dimensional (3D) structures with sub-micron precision. This enables innovative designs for optical microcavities and — lasers in view of applications such as chemical sensing. While the complexity of 3D structures enables new functionalities, it also increases the difficulty of understanding and designing resonator properties. Semiclassical methods based on periodic orbits (POs) are a promising solution. Experiments with flat 2D organic microlasers have shown the importance and usefulness of POs to understand and control their lasing properties [1], however, the extension of these methods to three dimensions remains a challenge.