Abstract. The unfavoured signature of the rotation-aligned band associated with the prolate h 9/2 structure in 187 Tl has been identified. The deformation-aligned 11/2 − [505] band is also confirmed and extended. While the alignment properties of the 11/2 − [505] band seem to indicate that it has a similar magnitude of deformation as the prolate 186 Hg core, the signature splitting at low spin, taken together with new self-consistent calculations, suggest that it may actually be triaxial with γ ≈ −18 0 near the bandhead.