Gastric leiomyosarcoma is a rare type of tumour that is far less prevalent than gastrointestinal stromal tumours. We describe a case of a 42-year-old male patient who consulted for upper abdominal pain. Blood work revealed low haemoglobin levels, requiring red blood cell transfusions. An esophagogastroduodenoscopy was performed, showing a submucosal tumour with central ulceration in the greater gastric curvature. The patient underwent an endoscopic ultrasound with fine needle biopsy and the sample showed a spindle cell neoplasia. Computed tomography scan demonstrated absence of distant metastases. Upon multidisciplinary consensus, it was decided to perform surgery. A laparoscopic approach was conducted, where no peritoneal lesions were observed. Transgastric resection of the tumour was performed. Free tumour margins were achieved following oncologic criteria (minimum tumour manipulation and one-piece resection without damaging the tumour capsule). After exhaustive sampling, the final pathology report informed an 11 × 9 × 5 cm gastric leiomyosarcoma. Immunohistochemical examination showed positivity with smooth muscle actin, muscle-specific actin, calponin and desmin. The patient had an uneventful recovery, and 6 post-operative months' clinical, tomographic and endoscopic control informed no disease recurrence. To the best of our knowledge, there are less than 20 published cases of patients with diagnosis of gastric leiomyosarcoma. This study highlights the importance of reporting this entity, in order to contribute to the available literature concerning this topic.