A method for positioning three translatable mirrors (B, C, D) in a laser gyrometer comprising three laser ring cavities, the positioning being carried out upon start-up of the gyrometer, each of the three laser cavities comprising: - an optical amplifier medium that can be excited so as to generate light waves; - an optical cavity (X, Y, Z) formed by a set of mirrors (A, B, C, D, E, F) including two of the translatable mirrors, the length of said optical cavity depending on the position of said two translatable mirrors, said two translatable mirrors being able to be displaced in ranges of positions providing the optical cavity with lengths at which the amplifier medium generates at least one laser wave, the mirrors being controlled by electric voltages so that their displacements are proportional to these voltages, each of the three translatable mirrors being used to form two of the three optical cavities, the method being characterised in that it comprises: - a phase of pre-positioning the three mirrors at an initial triplet of predetermined respective positions; - a phase of simultaneously translationally displacing the three mirrors in ranges with the same amplitude that is less than or equal to the intermode of the optical cavity with the highest intermode (K B, K C, K D), so as to ensure that each of the optical cavities passes through a length at which the amplifier medium provides a maximum gain, with the intensities of the laser waves respectively passing through each of the optical cavities being measured for each triplet of positions occupied by the mirrors, with the intermode being defined as the control voltage variation on one of the mirrors that allows the length of the corresponding cavity to be changed by an optical wavelength λ; - a phase of determining, based on the three triplets of positions of the mirrors that respectively allowed each of the three cavities to provide a maximum intensity, the length of each of the three cavities at which said cavity provides a maximum intensity; - a phase of determining a single final triplet of positions of the mirrors allowing the three cavities to be simultaneously provided with the lengths at which they provide a maximum intensity; - a phase of positioning the mirrors at the final triplet of positions. - an optical amplifier medium that can be excited so as to generate light waves; - an optical cavity (X, Y, Z) formed by a set of mirrors (A, B, C, D, E, F) including two of the translatable mirrors, the length of said optical cavity depending on the position of said two translatable mirrors, said two translatable mirrors being able to be displaced in ranges of positions providing the optical cavity with lengths at which the amplifier medium generates at least one laser wave, the mirrors being controlled by electric voltages so that their displacements are proportional to these voltages, - a phase of pre-positioning the three mirrors at an initial triplet of predetermined respective positions; - a phase of simultaneously translationally displacing the three mirrors in ranges with the same amplitude that is less than or equal to the intermode of the optical cavity with the highest intermode (K B, K C, K D), so as to ensure that each of the optical cavities passes through a length at which the amplifier medium provides a maximum gain, with the intensities of the laser waves respectively passing through each of the optical cavities being measured for each triplet of positions occupied by the mirrors, with the intermode being defined as the control voltage variation on one of the mirrors that allows the length of the corresponding cavity to be changed by an optical wavelength λ; - a phase of determining, based on the three triplets of positions of the mirrors that respectively allowed each of the three cavities to provide a maximum intensity, the length of each of the three cavities at which said cavity provides a maximum intensity; - a phase of determining a single final triplet of positions of the mirrors allowing the three cavities to be simultaneously provided with the lengths at which they provide a maximum intensity; - a phase of positioning the mirrors at the final triplet of positions.