AIM To observe the natural course of 1-3 cm gastric submucosal tumors originating from the muscularis propria(SMTMPs).METHODS By reviewing the computerized medical records over a period of 14 years(2000-2013), patients with 1-3 cm gastric SMTMPs who underwent at least two endoscopic ultrasound(EUS) examinations were enrolled. Tumor progression was defined as a ≥ 1.2 times enlargement in tumor diameter observed during EUS surveillance. All patients were divided into stationary and progressive subgroups and further analyzed. We also reviewed the patients in the progressive subgroup again in 2016.RESULTS A total of 88 patients were studied, including 25 in the progressive subgroup. The mean time of EUS surveillance was 24.6 mo in the stationary subgroup and 30.7 mo in the progressive subgroup. Risk factors for tumor progression included larger tumor size and irregular border. Initial tumor size > 14.0 mm may be considered a cut-off size for predicting tumor progression. Seventeen patients underwent surgery, of whom 13 had gastrointestinal stromal tumors(GISTs) and 4 had leiomyomas. Tumor progression was found only in patients with GISTs. All of the tumors exhibited benign behaviors without metastasis until 2016.CONCLUSION Most 1-3 cm gastric SMTMPs(71.6%) are indolent. Tumor progression was found only in GISTs, and it is a good predictor for differentiating GISTs from leiomyomas. Predictors of tumor progression include larger tumor size(> 14.0 mm) and irregular border. AIM To observe the natural course of 1-3 cm gastric submucosal tumors originating from the muscularis propria (SMTMPs). METHODS By reviewing the computerized medical records over a period of 14 years (2000-2013), patients with 1-3 cm gastric SMTMPs who underwent at least two endoscopic ultrasound (EUS) examinations were enrolled. Tumor progression was defined as a ≥ 1.2 times enlargement in tumor diameter observed during EUS surveillance. All patients were divided into stationary and progressive subgroups and further analyzed. in the progressive subgroup again in 2016.RESULTS A total of 88 patients were studied, including 25 in the progressive subgroup. The mean time of EUS surveillance was 24.6 mo in the stationary subgroup and 30.7 mo in the progressive subgroup. Risk factors for tumor progression included larger tumor size and irregular border. Initial tumor size> 14.0 mm may be considered a cut-off size for predicting tumor progression. Seventeen patien ts underwent surgery, of whom 13 had gastrointestinal stromal tumors (GISTs) and 4 had leiomyomas. Tumor progression was found only in patients with GISTs. All of the cultures buffet benign behaviors without metastasis until 2016. CONCLUSION Most 1-3 cm gastric SMTMPs ( 71.6%) are indolent. Tumor progression was found only in GISTs, and it is a good predictor for differentiating GISTs from leiomyomas. Predictors of tumor progression include larger tumor size (> 14.0 mm) and irregular border.