During measurements of the extrinsic spatial resolution of a gamma camera, it was noted that there was a variation with the position in the field of view. The problem was traced to the collimator, and this was confirmed by inspection of the parallel hole structure. Removal of the cover showed that the lead foil honeycomb had become detached from its surround. The fault could have had serious implications for the quality of patient investigations and could also have caused damage to the crystal if it had gone undetected. As a result of this investigation, the quality assurance procedures within this department have been updated to include a visual check of all collimator cores.