Hereditary mixed polyposis syndrome (HMPS) is a rare condition of unknown genetic origin. The paper presents 25-year clinical follow up in a female patient with multiple gastrointestinal tract polyps of varied histology. They most likely served as sites of multiple colorectal cancers development. The clinical course is interesting in terms of diagnostics and therapy. The patient required extended genetic testing, intensive conservative treatment and numerous surgical procedures. This is the first case of HMPS presented in Polish publications.