Nerve blocks are a key part of lameness investigation and remain the gold standard for localising lameness and assessing the significance of imaging findings. However, like any diagnostic test there is the potential for false positive and negative results and it is essential that the limitations of diagnostic analgesia are recognised. Inaccurate placement of local anaesthetic may lead to false negative results, particularly if the efficacy of a block cannot be fully assessed by testing skin sensation, and natural fluctuation of a lameness may lead to false positive results. Owners should be educated on the lack of reliability of diagnostic analgesia and if in doubt blocks should be repeated. The blocking pattern should always be related to the imaging findings and if the two do not agree then consideration should be given to diffusion of local anaesthetic or inaccurate placement.