Gastrointestinal stromal tumors (GISTs) are rare neoplasms (1%) of the gastrointestinal tract and to our knowledge only rare cases of synchronous presentation of gastric carcinomas and GISTs are reported in the literature. A 72-year-old female with a simultaneous presentation of gastric adenocarcinoma and GIST is presented. Moreover, due to polymyalgia rheumatica the patient received corticosteroids as treatment for the last 3 years. The concomitant occurrence of these neoplasms may involve common carcinogenic factors and there could be an association with polymyalgia rheumatica either as a paraneoplastic presentation or due to its treatment with corticosteroids.