Acanthamoeba keratitis is caused by protozoa and characterised by a protracted course. All patients presenting with a therapy-resistant keratitis, even non-contact lens wearers, should be examined for the presence of Acanthamoeba by means of specific cultures, histopathological stainings and--if necessary--a corneal biopsy. The combination of clinical signs, such as excessive pain, a radial keratoneuritis and in a later phase a stromal ring infiltrate, together with a suggestive history (contact lenses, polluted water) is an important factor for the early diagnosis. Because of improved clinical detection and earlier diagnosis, the infection can often be controlled with a combination therapy of polyhexamethylene biguanide or chlorhexidine with propamidine and neomycine. This results in a better visual prognosis and a decreased need for therapeutic keratoplasty.