This work characterizes interactive documentary as a native transmedia audiovisual format. This particular form of narrative expression often brings together and concentrates different media, formats and platforms through a metaphor and interactive navigation. Interactive documentary needs to fulfill a series of requirements to be considered a “native transmedia format”. This hypothesis is tested by selecting a set of representative projects and analyzing them for this purpose. First, we define and characterize the concept of transmedia narrative. Second, the concept of interactive and transmedia non-fiction is explored to bring into focus the specific narrative expression of interactive documentary. Third, we identify a small sample of projects from different countries. From this small sample, we chose the project Sexo, maracas y chihuahuas (Minimal Films, RTVE.ES, TVC, Labyrinz Studio, 2016) to be analyzed as a case study. We present the results, indicators and key structures determined in the qualitative analysis of the sample in the conclusions of the article. The three structures detected as the native transmedia format of interactive documentary are the “timeline structure”, the “container structure” and the “mosaic structure”. In the different projects analyzed, one type of structure predominates or thereis a mix of the three structures.