The purpose of this retrospective study was to evaluate the prognostic value of 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) in immunocompetent patients with primary central nervous system lymphoma (PCNSL). We also investigated whether FDG uptake was related to angiogenesis in the tumors. Seventeen patients with newly diagnosed and histologically confirmed PCNSL were investigated with FDG-PET before the treatment. FDG uptake was assessed by standardized uptake value of the tumor showing the maximum uptake (SUVmax). The Kaplan–Meier method was used to estimate the overall and the progression-free survival times. The difference of the survival curves between the low to moderate FDG uptake (SUVmax < 12) and high FDG uptake (SUVmax ≥ 12) groups was statistically analyzed. The relationship between FDG SUVmax and microvessel density (MVD) in the tumor specimens determined by CD34 immunohistochemical staining was examined. Finally, the difference of the overall survival curve between the low MVD (<20) and high MVD (≥ 20) groups was statistically analyzed. After the completion of initial treatment, 7 of the 8 low to moderate FDG uptake patients showed complete response (CR) and 1 showed partial response (PR). On the other hand, 5 of the 9 high FDG uptake patients showed CR and 4 showed PR. However, the difference of treatment response (CR vs PR) between the low to moderate and high FDG uptake groups was not statistically significant (P = 0.36). Median survival time was more than 26 months in low to moderate FDG uptake patients and 12 months in high FDG uptake patients. The overall survival time of patients with low to moderate FDG uptake was significantly longer than that of patients with high FDG uptake (P < 0.05). The progression free survival (PFS) was also significantly longer in patients with low to moderate FDG uptake compared to the patients with high FDG uptake (P < 0.05). There was no significant relationship between FDG SUVmax and MVD in the tumors. The survival time tended to be longer in patients with high MVD than in low MVD, but the difference was not statistically significant (P = 0.15). Pretreatment FDG uptake may have a prognostic value in newly diagnosed PCNSL.