Mycotic peritonitis can be demonstrated by microbiological, histological and serological tests. The disease can be proved histologically by a deep invasion of fungi. Initially, the mycotic peritonitis can be caused by polymicrobial infections and also by genuine mycotic invasion after perforation of the gastrointestinal tract. In the final phase of the disease only these fungi are of relevance. In most of the cases candida albicans can be verified. In the procedure of programmed peritoneal lavage the mycotic peritonitis provides a severe complication. Untreated, it would cause death by dissemination, fungemia and candida sepsis. 8 out of 12 patients with candida peritonitis died. Most of the patients had been severely ill previously and had shown several risk factors promoting mycotic disease. Antimycotic treatment has to be initiated as soon as possible, in order to diminish the high lethality.