Summary: A computer code written by the authors at the University of Coruña and aimed to produce optimum design of portal frames is presented in this paper. The PADO software provides the least weight design for the most common types of planar frames. The code incorporates the complete set of constraints considered in the Spanish code of practice for steel structures. The software has a graphical interface to provide a user-friendly communication. Some application examples are presented in this paper to make clear the capabilities of PADO code.