Dynamic OFDMA has been recognized as a promising technique forimproving the performance of future wireless cellularsystems. However, this potential performance improvement comes at thecost of additional signaling overhead, which can have a non-negligibleeffect on the system efficiency. In this paper, we propose a newmethod for optimizing the frame length for the downlink in OFDMAsystems. The method maximizes the system efficiency by taking intoaccount both the channel conditions and the amount of signalingoverhead needed to deliver scheduling maps to the users. We formulatethe frame length optimization problem mathematically. By exploitingthe structure of this problem, we develop an algorithm that solves asequence of dynamic programming problems. Simulation results revealsome insight into fundamental limitations as well as provide guidelinesfor the design of dynamic OFDMA systems.