This case report describes a rare side effect during a Bier's block. During local anaesthetic injection, the patient suffered a sudden onset painful petechial rash localised to the upper limb, distal to the tourniquet, without systemic effect. After deflation of the tourniquet, the pain resolved and no systemic effects were seen. The skin changes settled without treatment over one week. The discussion summarises standard technique and precautions required for a Bier's block. It also evaluates risks and complications.