This study investigates the effects of music training on brain activity to violations of melodic expectancies. We recorded behavioral and event-related brain potential (ERP) responses of musicians and nonmusicians to discrepancies of pitch between pairs of unfamiliar melodies based on Western classical rules. Musicians detected pitch deviations significantly better than nonmusicians. In musicians compared to nonmusicians, auditory cortical potentials to notes but not unrelated warning tones exhibited enhanced P200 amplitude generally, and in response to pitch deviations enhanced amplitude for N150 and P300 (P3a) but not N100 was observed. P3a latency was shorter in musicians compared to nonmusicians. Both the behavioral and cortical activity differences observed between musicians and nonmusicians in response to deviant notes were significant with stimulation of the right but not the left ear, suggesting that left-sided brain activity differentiated musicians from nonmusicians. The enhanced amplitude of N150 among musicians with right ear stimulation was positively correlated with earlier age onset of music training. Our data support the notion that long-term music training in musicians leads to functional reorganization of auditory brain systems, and that these effects are potentiated by early age onset of training.