An optoelectronic inclination sensor determines the inclination of a reference plane relative to the horizontal. A sensor body has a liquid layer, the free surface of which represents a horizon that can be inclined relative to the reference plane, forming an optical boundary to the adjacent medium. A light source disposed below the liquid layer emits a light beam onto the boundary. An optical sensor surface below the liquid layer detects the light beam reflected by the boundary. An analysis unit determines the inclination of the reference plane as a function of the amount of light received by the sensor surface. A deflecting element for deflecting or initially totally reflecting the beam is disposed between the source and the liquid layer. The beam is inclined as a result of said deflection or initial total reflection. A second total reflection occurs at the boundary in both the inclined and non-inclined orientation.