The identification of HER2 alterations in advanced gastric carcinomas is of critical importance in daily clinical practice as such neoplasms require specific treatment with trastuzumab. For these reasons, pathologists and oncologists with expertise in gastric carcinomas and HER2 testing from both organisations (SEAP and SEOM) have endeavoured to discuss and agree on national guidelines for HER2 testing in gastric carcinomas. These guidelines are based on the experience of those who participated in the discussions and also on experience published internationally. These agreed guidelines give the minimum requirements that a pathological anatomy laboratory must fulfil in order to guarantee adequate HER2 testing in daily practice. Any laboratories which do not meet the minimum standards set out in the guidelines must make every effort to achieve compliance.