We present for the first time optical (V, I and Gunn z) colour magnitude diagrams for Terzan 6, which were collected under excellent seeing conditions with the ESO NTT telescope. The horizontal branch morphology is red, nearly superimposed on the red giant branch. The red giant branch morphology presents characteristics intermediate between those of 47 Tuc and NGC 6528/NGC 6553. We derive a reddening of E(B-V)=2.24 and a distance d_{sun}_=7.0kpc (assuming R=3.1). We conclude that Terzan 6 belongs to the metal-rich bulge globular cluster system.