The angular distribution of thermal infrared (TIR) radiation emitted by vegetation covers can vary widely depending on environmental conditions and canopy structure. As an aid in the interpretation of TIR remotely sensed data from vegetated surface with incomplete canopies, we developed a three-dimensional radiative transfer model in the thermal infrared domain. The model simulates the TIR radiative budget and upward spectral radiance of vegetation covers. The model is an extension to the TIR region of the DART (Discrete Anisotropic Radiative Transfer) model developed for the short wave domain. Radiative transfer simulation relies on discrete 3-D scene representations, which include any distribution of trees and ground covers, possibly with topography. Propagation of emitted and scattered radiation is tracked with a ray-tracing approach and the discrete ordinate method. The model was successfully tested against a physically based model for homogeneous canopies, and a partial validation was carried out with directional TIR measurements on a cotton row crop. Model simulations are presented to illustrate the influence of the canopy geometric structure on the directional apparent temperature of hypothetical vegetation covers.