We report the discovery of 1RXS J173006.4+033813, a polar cataclysmic variable with a period of 120.21 min. The white dwarf primary has a magnetic field of B = 42+6-5 MG, and the secondary is a M3 dwarf. The system shows highly symmetric double peake
d photometric modulation in the active state as well as in quiescence. These arise from a combination of cyclotron beaming and ellipsoidal modulation. The projected orbital velocity of the secondary is K2 = 390+-4 km/s. We place an upper limit of 830+-65 pc on the distance.
