This paper presents a microfabricated impedance spectroscopy flow cytometer which permits rapid and easy dielectric characterization of cells as they flow in a microchannel. Both a simple theoretical model and a finite element simulation show that the effects of particle size dominate the entire spectrum. Dielectrophoretic forces are used to focus polystyrene beads along the centerline of the channel and decrease the spread in signal amplitude. Measurements of the beads show that size differences of less than 1 gm diameter can be discriminated.