  We present distance measurements to 71 high redshift type Ia supernovae
discovered during the first year of the 5-year Supernova Legacy Survey (SNLS).
These events were detected and their multi-color light-curves measured using
the MegaPrime/MegaCam instrument at the Canada-France-Hawaii Telescope (CFHT),
by repeatedly imaging four one-square degree fields in four bands. Follow-up
spectroscopy was performed at the VLT, Gemini and Keck telescopes to confirm
the nature of the supernovae and to measure their redshift. With this data set,
we have built a Hubble diagram extending to z=1, with all distance measurements
involving at least two bands. Systematic uncertainties are evaluated making use
of the multi-band photometry obtained at CFHT. Cosmological fits to this first
year SNLS Hubble diagram give the following results : Omega_M = 0.263 +/-
0.042(stat) +/- 0.032(sys) for a flat LambdaCDM model; and w = -1.023 +/-
0.090(stat) +/- 0.054(sys) for a flat cosmology with constant equation of state
w when combined with the constraint from the recent Sloan Digital Sky Survey
measurement of baryon acoustic oscillations.
