A key ingredient to searches for physics beyond the Standard Model in Bs-0 mixing phenomena is the measurement of the B s-0 oscillation frequency, which is equivalent to the mass difference Δms of the Bs-0 mass eigenstates. Using the world's largest Bs-0 meson sample accumulated in a dataset, corresponding to an integrated luminosity of 1.0 fb-1, collected by the LHCb experiment at the CERN LHC in 2011, a measurement of Δms is presented. A total of about 34 000 B s-0 → Dsπ-+ signal decays are reconstructed, with an average decay time resolution of 44 fs. The oscillation frequency is measured to be Δms = 17.768 ± 0.023 (stat) ± 0.006 (syst) ps-1, which is the most precise measurement to date. © CERN 2013 for the benefit of the LHCb Collaboration, published under the terms of the Creative Commons Attribution 3.0 licence by IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Any further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation and DOI..