The thermally activated resistivity, r_xx, and the negative Hall resistivity, r_xy are explained as two consequences of the same effect, namely the unbinding of vortex pairs in the vicinity of T_c. Both r_xx and r_xy exhibit a thermally activated behaviour. The activation energy depends logarithmically on the magnetic field. Our explanation suggests r_xy ∼ r_xx^a with a = 1 in accordance with recent measurements.