The ATLAS collaboration has chosen for the electromagnetic barrel calorimeter and for all the end-cap calorimeters a sampling technique, with liquid argon as the active medium. The read-out electronics and the calibration pulsers are located in boxes outside the cryostats housing the detectors. Signals are transmitted between the detectors and the electronic boxes through custom-designed micro-coaxial cables, which are the subject of this paper. These cables have to satisfy very stringent tolerances in terms of signal transmission, dimensions and radiation hardness. Following a successful pre-series production, these cables have been selected for equipping the ATLAS calorimeter.