Giardiasis is a cosmopolitan parasitic disease. About 10% of adults and 20% of children in Poland is infected with Giardia lamblia but only a few per cent of cases is symptomatic. Incidence and symptomatology depend upon a number of factors including individual susceptibility. The disease is usually chronic and recurrent and acute form is found in rare cases only. Giardiasis should be suspected in patients with chronic atypical symptoms related to the alimentary tract. Nitroimidasolic compounds are used in the treatment of giardiasis.