A first prototype of a high resolution small animal PET scanner based on continuous LYSO scintillator crystals and silicon photomultiplier matrices has been developed at IFIC Valencia, in collaboration with the University of Pisa and INFN Pisa. The prototype consists of two detector heads attached to a rotating stage. Each head is composed of a continuous 12mm × 12mm × 5mm LYSO crystal painted white, coupled to a monolithic SiPM matrix. The matrices, developed at FBK-irst, are composed of 8×8 SiPM elements of 1.5 mm×1.4 mm size in a common substrate. The full characterization of the detector heads with different types of crystals has been carried out, and a method for determining the interaction position of the gamma-rays in the crystals has been successfully employed. Tomographic data have been acquired with the prototype, and images of different source distributions have been reconstructed with the Maximum Likelihood Expectation Maximization algorithm (MLEM). A FWHM close to 1 mm is obtained for one and two point-like sources.