An optical system of a stereo video endoscope with lateral viewing direction. The optical system including: a sideways looking distal optical assembly and a proximal optical assembly. Where the distal optical assembly includes, successively in a direction of light incidence on a common optical axis: an entrance lens configured as a raised negative meniscus, an optical deflection unit and an exit lens configured as a hollow positive meniscus, Where the distal optical assembly has, at least in sections, a right and a left lens system channel of identical type and arranged parallel to one another, each of the right and left lens system channel having: a dedicated optical axis, and at least one first lens and an achromatic lens group in the direction of light incidence.
