Sodium hypochlorite (NaOCl) in various concentrations is the most widely used root canal irrigant, but it can be an irritant to vital tissue. There are several reports about complications of root canal irrigation with NaOCl. Most of them are the result of accidental extrusion beyond the apex. The inadvertent injection of NaOCl instead of local anaesthetic solution is an extremely rare misuse and results in severe problems. The consequences of the inadvertent injection of sodium hypochlorite, precautions to avoid such accidents and also treatment options are discussed. Sodium hypochlorite is highly irritating when introduced into oral tissues. To avoid inadvertent injection of sodium hypochlorite during root canal treatment, NaOCl solutions should be prepared in special syringes, which are clearly distinguishable from syringes used for other solutions or anaesthetics. Lower concentration NaOCl solutions should be preferred to higher or full-strength solutions. Keywords: ecchymosis, haematoma, oedema, paraesthesia, tissue necrosis