Gastrointestinal stromal tumors are the most common mesenchymal neoplasms of the gastrointestinal tract. Most cases of GISTs occur sporadically. In spite of that, the coexistence of other primary tumors in GIST patients is not a rarity. These tumors can occur in the same time (synchronously) or before/after (metachronously) in regards to GIST. In this thesis, we analyzed KB Dubrava's archive from 2000. to 2016. and noted all GISTs. We analyzed medical records and found 100 patients with GISTs. Additional 44 primary tumors have been found in 35 (out of 100) patients with GIST. There were 20 (45%) cases of synchronous and 24 (55%) cases of metachronous neoplasms. The most common were gastrointestinal neoplasms (15 cases, 34%) and neoplasms of genitourinary tract (10 cases, 23%). The average size of GIST was 3.82 cm in the group of patients with additional neoplasms, which is less than those in patients without additional tumors (6.60 cm). In the group with additional tumors, 37% of patients had GIST that were classified as prognostic group 1 according to classification of gastrointestinal tumors by World Health Organisation from 2010., which is significantly higher when compared to the group of patients without additional neoplasms (9%). Furthermore, GIST has more often been an incidental finding in the group with additional neoplasms, than in patients without additional synchronous or metachronous primary tumors. In conclusion, we found a 35% prevalence of synchronous and metachronous tumors in a group of 100 patientes, which indicates that the presence of additional primary tumors in GIST patients is not uncommon, and should be kept in mind during diagnosis, treatment and monitoring of patients.