We provide an exact analysis of orthogonal frequency-division multiplexing (OFDM) performance in the presence of phase noise. Unlike most methods which assume small phase noise, we examine the general case for any phase noise levels. After deriving a closed-form expression for the signal-to-noise-plus-interference ratio (SINR), we exhibit the effects of phase noise by precisely expressing the OFDM system performance as a function of its critical parameters. This helps in understanding the meaning of small phase noise and how it reflects on the proper parameters selection of a specific OFDM system. In order to combat phase noise, we also provide in this paper a general phase-noise suppression scheme, which, by analytical and numerical results, proves to be quite effective in practice.