The system NdBr3(s)-NdI3(s) has been studied by differential thermal analysis (DTA) and X-ray diffraction analysis. At room temperature, NdBr3(s) and NdI3(s) have an orthorhombic structure (space group Cmcm). For the lattice parameters, the values a = 0.4131 nm, b = 1.2765 nm, and c = 0.9192 nm, and a = 0.4296 nm, b = 1.4060 nm, and c = 0.9971 nm are found, respectively. A phase transition in NdI3(s) at (859.3 +/- 0.6) K was observed, resulting in a complex phase diagram of a eutectic system and two solid-solubility regions.