Structures experience lateral deflections under earthquake loads. Magnitude of these lateral deflections is related to many variables such as structural system, mass of the structure and mechanical properties of the structural materials. Buildings should be designed so that they can resist earthquake induced deflections and internal forces. Structural irregularities are important factors which decrease the seismic performance of the structures. Buildings which have structural irregularities may experience different drifts of adjacent stories, excessive torsion, etc. according to irregularity type and fail during an earthquake. In this paper, effects of torsional irregularity on structures are studied. Building models, which have different number of floors and floor areas, are generated by a computer program and calculations are made. Results are compared and precautions are given to prevent damages caused by torsional irregularity under earthquake loads. Also, statements in different earthquake codes about torsional irregularity are compared. Calculations show that separating big building sections from each other with proper separation distances and increasing lateral rigidity on the weak direction of the structures decrease the effect of torsion. (C) 2013 Elsevier Ltd. All rights reserved.