Neuroendocrine (NE) lung tumors are subdivided into the following types; typical (TC) and atypical carcinoids (AC), large cell neuroendocrine carcinoma (LCNEC), and small cell lung carcinoma (SCLC). Moreover, the determinants of the FDG uptakes of NE lung tumors have not been elucidated. Thus, the aim of the present study was to investigate the relationships between FDG uptake and glucose transporter type 1 (Glut-1) expression in these NE tumors. Tissue-proven NE lung tumor patients (n=32; age, mean+/-S.D.=67.8+/-10 years; male:female=28:4) who had undergone F-18 FDG-PET before treatment were enrolled in this study. There were 1 TC, 3 AC, 5 LCNEC, and 23 SCLC patients. FDG uptakes were quantified using maximum standardized uptake values (maxSUV). Paraffin sections of tumor tissues were immunostained using anti-Glut-1 antibody (Neomarkers, 1:50). Levels of Glut-1 expression are presented as percentages of tumor cells positively immunostained (%Glut-1). Relations between FDG uptakes and Glut-1 expression were assessed using Pearson correlation analysis. The maxSUVs of all NE lung tumors ranged from 0.6 to 29.5 (mean+/-S.D.=7.7+/-5.4) and %Glut-1 expression ranged from 0 to 100% (18+/-24%). The maxSUVs of all NE lung tumors were found to be significantly correlated with %Glut-1 expression (r=0.6471, p=0.0001). By subgroup analysis, maxSUV was also found to be significantly correlated with %Glut-1 expression in SCLC (n=23, r=0.6189, p=0.0016). FDG uptake was found to be highly correlated with Glut-1 expression in NE lung tumors. This result suggests that Glut-1 plays a crucial role in determining FDG uptake in these tumors.