Using x-ray diffuse scattering, we have observed enhanced Kohn anomalies in the two-dimensional conductor Ta0.9Hf0.1S2. From this, we have deduced the shape of the Fermi surface of this compound throughout a wide region of reciprocal space. The results in the (h0l) planes demonstrate the two-dimensionality of the electronic states in this substance. The results in the layers h, k, 13 prove that the topographic shape originally postulated by Williams, Parry, and Scruby is correct. © 1975 The American Physical Society.