This paper introduces the 3DNFDM, an extension of the Natural Force Density Method (NFDM) to three dimensional problems. The NFDM was first proposed by Pauletti in 2006, as a method for finding configurations of membranes and funicular shell structures, providing viable equilibrium geometries in a single linear equilibrium analysis. It is an extension of the Force Density Method (FDM), which was originally proposed by Linkwitz and Schek in 1971 for the shape finding of cable-nets and has since become ubiquitous in the field of membrane design. Since its proposition, the NFDM has found a relevant niche on the design of membranes and funicular shells, being independently incorporated into some computer programs, and referred to by several independent research. In this paper we describe an extension of the NDFM to three dimensional problems, which generates a novel class of shape finding problems. The new method, called 3DNFDM, generates viable volumetric shapes, some of which are not readily interpreted by common sense. The correlation between the 3DNFDM to the previous FDM and NFDM methods and the basic properties of the new method are explored through some elementary benchmarks. We believe the new method opens perspectives for new research, on problems such as thick vaults and shells shape finding and analysis, design of tunnels and excavations, or of material inclusions, or perhaps other so far unforeseen applications.