Synchrotron x-ray diffraction and absorption, together with magnetic and thermoelectric measurements, have been used to investigate the mechanism driving the metal to insulator transition in YBaCo2O5.50. Results show a structural and magnetic transition concomitant with the metal to insulator transition. Absorption spectroscopy at the Co L3 edge as a function of temperature reveals minor changes across the transition. The set of experimental results are hardly conciliative with a high to low spin state change of Co ions at octahedral sites in this cobaltite.