In a method for producing at least a single-walled tubular thermoplastic body in a machine, a nozzle head extrudes at least one tubular preform. The preform is expanded to a predefined dimension in a transverse direction and to a predefined shape in an expansion process using an expanding mandrel, the preform remaining open at the top and bottom. When the at least one preform has cooled off, the expanding mandrel is changed into a non-expanded state and the at least single-walled tubular body is removed from the machine.