The Italian research foundation TERA has proposed an innovative accelerator solution, called “Cyclinac” [1], dedicated to hadrontherapy, the technique of tumor radiotherapy which employs ion beams, in particular protons and carbon ions. It is composed of a fixed-energy cyclotron injecting into a variable-energy linac. This paper describes the preliminary design of a dedicated superconducting synchrocyclotron providing fast cycling (400 Hz) beams of 230 MeV/u C6+ and H2 + (Kbending = 920 MeV).