The first precise measurement of the B0(s)-\bar{B}0_s
oscillation frequency Delta m_s with the CDF II experiment is summarized in
this talk.  The measurement is performed with 1 fb-1 of data collected at
the Fermilab Tevatron hadron collider.  We find a signal consistent with
flavour oscillations; the probability that such a signal is originated by
random fluctuations is 0.2%.  We measure Delta m_s =
17.31+0.33_-0.18(stat.) +/- 0.07(syst.)ps-1 [1].  After a brief
theoretical overview, I will describe the experimental technique and show
the results of the CDF analysis and the |V_td/V_ts| value we infer from this
measurement.