We propose a three-dimensional-local directional pattern (3D-LDP) computation method in this study for early diagnosis of Alzheimer's disease. The proposed 3D-LDP is defined as a 1-bit decimal pattern which is calculated by computing and comparing edge response values in 18 directions. By concatenating three individual histograms extracted from three segmented sub-regions of grey matter, the accuracy, sensitivity, and specificity of the proposed 3D-LDP method were obtained as 81, 84, and 79%, respectively, comparable or even better than those of the existing 3D-LTP method (80, 85, and 78%).