The aim of this study, was to investigate the relationship between (18)F-fluorodeoxyglucose ((18)F-FDG) uptake in primary tumors and the clinicopathological characteristics of esophageal squamous cell carcinoma (ESCC) patients. Patients with histopathologically diagnosed ESCC who had received a pre-therapeutic (18)F-FDG positron emission tomography-computed tomography (PET-CT) scan were enrolled in the study. The maximum standardized uptake value (SUVmax) and the length of the primary tumor were measured by PET-CT. The clinical tumor-node-metastasis (TNM) stage was determined mainly by PET-CT images according to the American Joint Committee on Cancer (AJCC) staging system, 2002. A significant difference was observed in SUVmax between the length and T stage of the primary tumor (P=0.000 and P=0.017, respectively), but not in the grade of tumor differentiation (P=0.383), clinical stage (P=0.583), N staging (P=0.387), M staging (P=0.886), patient age (P= 0.752) or gender (P=0.233). There was a significant positive correlation between the SUVmax and the length of the tumor (r=0.456, P=0.000) and the depth of invasion of the primary tumor (r=0.257, P=0.006). After controlling for length, no statistically significant correlation was found between T stage and SUVmax (r=0.074, P=0.537). In conclusion, these findings suggest that tumor length influences FDG uptake in ESCC tumors, and that the T stage of the primary tumor is not significantly correlated with the SUVmax after controlling for length. However, we did not find a significant correlation between the SUVmax and primary tumor differentiation and clinical stage. These data provide important information for the management of ESCC.