Knowledge on autoregulation of cerebellar blood flow in humans is scarce. This study investigated whether cerebellar autoregulation dynamics and CO(2) reactivity differ from those of the supratentorial circulation. In 56 healthy young adults, transcranial Doppler (TCD) monitoring of the posterior inferior cerebellar artery (PICA) and, simultaneously, of the contralateral middle cerebral artery (MCA) was performed. Autoregulation dynamics were assessed by the correlation coefficient method (indices Dx and Mx) from spontaneous blood pressure fluctuations and by transfer function analysis (phase and gain) from respiratory-induced 0.1 Hz blood pressure oscillations. CO(2) reactivity was measured via inhalation of air mixed with 7% CO(2). The autoregulatory indices Dx and Mx did not differ between the cerebellar (PICA) and cerebral (MCA) vasculature. Phase and gain, which describe faster aspects of autoregulation, showed slightly better values in the PICA compared with the MCA (higher phase, P=0.005; lower gain, P=0.007). Correlation between absolute autoregulation values in the PICA and the MCA was significant (P<0.001). The TCD CO(2) reactivity was significantly lower in the PICA (P<0.001), which could be influenced by an assumed PICA dilation under hypercapnia. In conclusion, dynamic autoregulation in the human cerebellum is well operating and has slightly faster regulatory properties than the anterior cerebral circulation.