Objectives: BioNTech (Pfizer) and CoronaVac (Sinovac) vaccines are two of the most administered coronavirus disease-2019 (COVID-19) vaccines worldwide. Vaccination against severe acute respiratory syndrome-coronavirus-2 has caused a diagnostic challenge in oncological 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) studies. The aim of our study was to evaluate the 18F-FDG PET/CT findings of the two most commonly administered vaccines worldwide. Methods: Patients over 18 years old who underwent 18F-FDG PET/CT for oncological purposes in our institution between January 13, 2021 and January 31, 2022, who received a single or second dose of the BioNTech or CoronaVac vaccines in the last two months, were included in the study. Descriptive analyses were presented as mean, standard deviation, frequency and ratio. Additionally, chi-square test was used to analyze categorical variables. Results: Ipsilateral deltoid muscle hypermetabolism was observed in 6.9% (n=15) and 14.3% (n=22) patients who received CoronaVac and BioNTech vaccines, respectively. Ipsilateral axillary lymph node hypermetabolism was observed in 11% (n=24) and 41.6% (n=64) patients who received CoronaVac and BioNTech vaccines, respectively. Synchronous deltoid muscle and axillary lymph node hypermetabolism was observed in 4.14% (n=9) and 12.33% (n=19) patients who received CoronaVac and BioNTech vaccines, respectively. Significant differences were detected between CoronaVac and BioNTech vaccines in terms of ipsilateral deltoid muscle hypermetabolism, ipsilateral axillary lymph node hypermetabolism and synchronous deltoid muscle and axillary lymph node hypermetabolism (p<0.05). Conclusion: COVID-19 vaccination may result in ipsilateral axillary lymph node hypermetabolism, ipsilateral deltoid muscle hypermetabolism, or synchronous deltoid muscle and axillary lymph node hypermetabolism with different frequencies depending on the type of vaccination. Although synchronous deltoid muscle and axillary lymph node hypermetabolism can reduce misinterpretation of 18F-FDG PET/CT, to avoid misinterpretation, it is important to question the vaccination history during ongoing COVID-19 vaccination process.