An approximate method to estimate the maximum lateral deformation demands in multistory buildings responding primarily in the fundamental mode when subjected to earthquake ground motions is presented. This method permits a rapid estimation of the maximum roof displacement and of the maximum interstory drift for a given acceleration time history or for a given displacement response spectrum. A multistory building is modeled as an equivalent continuum structure consisting of a combination of a flexural cantilever beam and a shear cantilever beam. The simplified model is used to investigate the ratio of the spectral displacement to the roof displacement and the ratio of the maximum interstory drift ratio to the roof drift ratio. The effect of the distribution of lateral forces along the height of the building and of the ratio of overall flexural and shear deformations is examined. Lateral deformation demands of a 10-story steel building computed with the simplified method when subjected to various earthquake ground motions are compared with those computed using stepby-step time history analyses. It is shown that the method provides good approximations, which are useful for the preliminary design of new buildings or for a rapid evaluation of existing buildings.