A first analysis of the complete set of data collected by CHORUS in the yea
rs 1994-1997 is presented. The search for nu (tau) charged current events h
as been performed for both leptonic and hadronic decays of the tau lepton.
No tau candidate has been found, A nu (tau) --> nu (tau) mixing is excluded
down to sin(2)2 theta (mu tau) = 6.8 x 10(-4) for large Deltam(2) (90% C.L
.). (C) 2001 Elsevier Science B.V. All rights reserved.