Mooren's ulcer is strictly a peripheral ulcerative keratitis (PUK) with no associated scleritis. It occurs completely in absence of any diagnosable systemic disorder that could be responsible for the progressive destruction of the cornea. The aetiology of Mooren's ulcer remains uncertain. However, recent studies indicate that it is an autoimmune disease directed against a specific target molecule in the corneal stroma, probably triggered in genetically susceptible individuals by one of several possible provocateurs. Advances have been made in the management of this disease. Immunosuppressive therapy has been shown increasingly successful in patients unresponsive to conventional treatment and in bilateral progressive destructive ocular disease.