The invention concerns a sensor and a method for detecting microbiologically induced corrosion in a metal structure, which consists in performing the following steps: providing a sensor comprising at least a first circular electrode (4) and a ring-shaped electrode (2) concentric with the first electrode, proximate to the structure (30) in contact with a corrosive medium; imparting for a time interval t a conditioning current between the two electrodes so as to initiate corrosion, the current being such that the central electrode is cathode and the ring-shaped electrode is anode; after the time interval t, coupling the two electrodes and measuring the current between the two electrodes; calculating the speed of corrosion from the measurement.