System for purposes of temperature monitoring when executing a laser light-based lithotripsy, in which an endoscope arrangement is used, which comprises an operating channel for a light guide, which on the proximal side is optically coupled to a laser, and on the distal side has a light exit aperture, together with a flushing fluid channel, which on the distal side opens out in the region of the light exit aperture, and on the proximal side is fluidically connected to a flushing fluid reservoir, characterised in that, the system provides a modular unit that can be combined with the endoscope arrangement, which modular unit comprises the following components: a flow rate sensor, which can be mounted longitudinally on the flushing fluid channel, and/or on a supply line fluidically connected to the flushing fluid channel, and determines a flushing flow rate without contact with the flushing fluid, an input means, by way of which, operating parameters of the laser, on the basis of which a laser power can be applied at the location of the light emission aperture, can be determined, can be transmitted to a computer unit connected to the input means, a temperature sensor, which can be mounted longitudinally on the flushing fluid channel, and/or on a supply line fluidically connected to the flushing fluid channel, and which determines a temperature of the flushing fluid without contact with the flushing fluid, an evaluation unit implemented in the computer unit, which evaluation unit numerically determines a temperature T forming intracorporeally at the location of the light emission aperture during the laser light-based lithotripsy, at least on the basis of the flushing flow rate, the temperature of the flushing fluid (T s) and the determined applied laser power, together with a comparator unit, which compares the determined temperature T with a threshold value and generates a signal if the threshold value is exceeded. a flow rate sensor, which can be mounted longitudinally on the flushing fluid channel, and/or on a supply line fluidically connected to the flushing fluid channel, and determines a flushing flow rate without contact with the flushing fluid, an input means, by way of which, operating parameters of the laser, on the basis of which a laser power can be applied at the location of the light emission aperture, can be determined, can be transmitted to a computer unit connected to the input means, a temperature sensor, which can be mounted longitudinally on the flushing fluid channel, and/or on a supply line fluidically connected to the flushing fluid channel, and which determines a temperature of the flushing fluid without contact with the flushing fluid, an evaluation unit implemented in the computer unit, which evaluation unit numerically determines a temperature T forming intracorporeally at the location of the light emission aperture during the laser light-based lithotripsy, at least on the basis of the flushing flow rate, the temperature of the flushing fluid (T s) and the determined applied laser power, together with a comparator unit, which compares the determined temperature T with a threshold value and generates a signal if the threshold value is exceeded.