Summary. Gastrointestinal stromal tumours (GIST) may be defined as intraabdominal mesenchymal tumours that express KIT protein or have an activating mutation in class III receptor tyrosine kinase gene (KIT or PDGFRa). Most GISTs respond to imatinib mesylate, which selectively inhibits both KIT and PDGFRa, and is now considered standard systemic therapy for advanced GIST. We assessed the antitumour response of patients treated with imatinib mesylate who had advanced and/or metastatic (GIST). In the Department of Medical Oncology fourteen (14) patients with advanced GIST were treated in the period from year 2002 to 2004. Imatinib mesylate was applied at the dose of 400 mg daily. Only two patients required dose enlargement up to 800 mg. All tumours had positive immunohystochemical expression of KIT. Median age of patients was 56 years. 12 male patients and 2 female patient was treated. Considering primary site of tumour we had 6 small intestine, 4 mesenterium and 4 gastric tumours. Mean duration of the treatment was 14 months (5 to 30 months). Six patients had partial remission, six had stable disease and two progression. Complete remission has not been achieved in any patient. Side-effects were mild and no patient required dose reduction or treatment discontinuation. Our results show the effectivness of targeted antitumour therapy with imatinib mesylate in advanced and/or metastatic GIST, and correspond to those in literature.