We present phenomenological predictions for the cutoff frequency of carbon nanotube transistors. We also present predictions of the effects parasitic capacitances on AC nanotube transistor performance. The influence of quantum capacitance, kinetic inductance, and ballistic transport on the high-frequency properties of nanotube transistors is analyzed. We discuss the challenges of impedance matching for ac nano-electronics in general, and show how integrated nanosystems can solve this challenge. Our calculations show that carbon nano-electronics may be faster than conventional Si, SiGe, GaAs, or InP semiconductor technologies. We predict a cutoff frequency of 80 GHz/L, where L is the gate length in microns, opening up the possibility of a ballistic THz nanotube transistor. (C) 2004 Elsevier Ltd. All rights reserved.