The problem of modeling periodic signals is considered. The approach taken here is motivated by the well known theoretical results on the existence of periodic orbits for Lienard systems and previous results on modeling periodic signals by means of second-order nonlinear ordinary differential equations. The approach makes use of the appropriate conditions imposed on the polynomials of the Lienard's system to guarantee the existence of a unique and stable limit cycle. These conditions reduce the number of parameters required to generate accurate models.