This paper presents a method for robust volumetric texture classification. It also proposes 2D and 3D gradient calculation methods designed to be robust to imaging effects and artifacts. Using the proposed 2D method, the gradient information is extracted on the XYZ orthogonal planes at each voxel and used to form a local coordinate system. The local coordinate system and the local 3D gradient computed by the proposed 3D gradient calculator are then used to define volumetric texture features. It is shown that the presented gradient calculation methods can be efficiently implemented by convolving with 2D and 3D kernels. The experimental results demonstrate that the proposed gradient operators and the texture features are robust to imaging effects and artifacts, such as blurriness and noise in 2D and 3D images. The proposed method is compared with three state-of- the-art volumetric texture classification methods the 3D gray level cooccurance matrix, 3D local binary patterns, and second orientation pyramid on magnetic resonance imaging data of the brain. The experimental results show the superiority of the proposed method in accuracy, robustness, and speed.