Assessments of spatial, constructional ability are used widely in cognitive research and in clinical diagnosis of disease or injury. Some believe that three-dimensional (3D) forms of these assessments would be particularly sensitive, but difficulties with consistency in administration and scoring have limited their use. We describe Cognitive Cubes, a novel computerized tool for 3D constructional assessment that increases consistency and promises improvements in flexibility, reliability, sensitivity and control. Cognitive Cubes makes use of ActiveCube, a novel tangible user interface for describing 3D shape. In testing, Cognitive Cubes was sensitive to differences in cognitive ability and task, and correlated well to a standard paper-and-pencil 3D spatial assessment. Keywords Cognitive assessment, neuropsychological assessment, tangible user interfaces, three-dimensional user interfaces, constructional ability, spatial ability