In the LHCb experiment at the Large Hadron Collider, powerful charged particle identification is performed by Ring Imaging CHerenkov (RICH) technology. In order to cover the full geometric acceptance and the wide momentum range (1–100 GeV/ c), two detectors with three Cherenkov radiators have been designed and installed. In the medium (10–40 GeV/ c) and high (30–100 GeV/ c) momentum ranges, gas radiators are used (C 4F 10 and CF 4, respectively). In the low momentum range (1–10 GeV/ c), pion, kaon and proton separation is performed with solid silica aerogel radiator. A set of 16 tiles, with large transverse dimensions of up to 200 × 200 mm 2 and nominal refractive index 1.03 have been produced and integrated in the detector. These tiles have excellent optical properties and homogeneity of the refractive index at the percent level within the tile. The first data collected at the LHC are used to investigate the behaviour of the RICH; preliminary results of the performance of silica aerogel are presented and discussed.