Performance of CMS ECAL with first LHC data

In the CMS experiment at the CERN LHC, the high resolution Electromagnetic Calorimeter (ECAL), consisting of 75848 lead tungstate crystals and a silicon/lead preshower, will play a crucial role in the physics program. In preparation for the data taking, a detailed procedure was followed to commission the ECAL readout and trigger, and to pre-calibrate, with test beam and cosmic ray data, each channel of the calorimeter to a precision of 2$\%$ or less in the central region. The first LHC collisions have been used to complete the detector commissioning and will provide the first in-situ calibration. In this talk the CMS ECAL status and performance with the first collisions delivered from LHC will be reviewed.