The crystal structure of the title compound, C(5)H(3)BrN(2)S, shows that bromination of 1H-thieno[2,3-d]imidazole with N-bromo-succinimide in acetonitrile occurs at position 5 of the bicyclic system. The mol-ecule is almost planar, with a mean deviation of 0.015 Å from the least-squares plane through all the non-H atoms. In the crystal, N-H⋯N hydrogen bonds link the mol-ecules into infinite C(4) chains running along [101].