Diagrid structures are widely used for today’s tall buildings due to their distinguished architectural aesthetics in any existing urban context and structural efficiency in carrying lateral loads. With prevalent emergence of complex-shaped buildings throughout the world, this paper investigates structural efficiency of diagrid structures employed for complex-shaped tall buildings, such as twisted, tilted and freeform towers. For each complex form category, tall buildings are designed with diagrid systems, and their structural efficiency is studied in conjunction with building forms. In order to investigate the impacts of various important geometric configurations of complex-shaped tall buildings, parametric models are generated using appropriate computer programs, and the models are exported to structural engineering software for design and analyses. Based on the study results, structural efficiency of diagrids for tall buildings of each complex form category is estimated.