Disability assessment is a complex process that requires consideration of both work demands and clinical conditions. It is commonly practiced in two very distinct fashions. First, poorly specified processes are used to reach decisions about highly specific situations; second, broad generalizations are often applied, which may be poorly applicable to specific situations. A new approach allows the integration of these two methods. The "atomic" approach has two phases: "disaggregation" into the smallest possible meaningful knowledge units (atoms) and then "reintegration" (reassembly). Individual information units may be applicable to a wide variety of different situations, providing an efficient system. The atomic approach includes two tracks that merge to produce the dis/ability assessment: Clinical track (diagnosis-->confirmation test; diagnosis-->impact assessment test-->test result-->physiologic/anatomic limitation; and the job demand track (job-->task-->sub task-->functional work demand index-->empiric data). The approach describe offers advantages of rationality, empiric and face validity, and efficiency. The logic is fully explicable, and most information units (atoms) can be used in many ways to cover new situations. It is applicable to both individual case situations and to large-scale system development.