We have applied atom probe tomography (APT) to analyze self-organizing structures of wear-resistant Zr0.69Al0.31N thin films grown by magnetron sputtering. Transmission electron microscopy shows that these films grow as a three-dimensional nanocomposite, consisting of interleaved lamellae in a labyrinthine structure, with an in-plane size scale of similar to 5 nm. The structure was recovered in the Al APT signal, while the Zr and N data lacked structural information. The onset of the self-organized labyrinthine growth was observed to occur by surface nucleation, 5-8 nm above the MgO substrate, due to increasing Zr-Al compositional fluctuations during elemental segregation. At a final stage, the labyrinthine growth mode was observed to be interrupted by the formation of larger ZrN grains. (C) 2016 Elsevier B.V. All rights reserved.