Large tissue regions are treated using pairs of electrode arrays. The electrode arrays may be concave and disposed in tissue so that their concave portions are opposed to each other. Axial conductors may be provided extending from the arrays and toward each other in order to increase the heating of tissues lying along the axis between the deployed electrode arrays. By properly spacing the electrode arrays apart and selecting the diameters of the arrays, desired volumes of tissue may be treated, typically with a bipolar, radiofrequency current.