This study aimed to identify the neural networks underlying automatic and active auditory deviant detection in six healthy subjects using positron emission tomography. Eight alternating blocks of standard and standard plus duration-deviant tones were presented while subjects performed a visual discrimination task. In an additional four blocks, the subjects then performed an auditory discrimination task on the deviant tones. Actively attending the deviant tones increased regional cerebral blood flow (rCBF) in the superior temporal and inferior frontal gyrus as well as in the superior and medio-frontal gyrus. When performing the visual task and presented with deviant tones, significant increase of rCBF was detected in the caudate nucleus, cerebellum, posterior cingulate, inferior frontal and pre-central gyrus thus indicating automatic extra-pyramidal processing of auditory duration deviants.