<h3>Purpose/Objective(s)</h3> The assessment of the prevalence of retro-styloid lymph node metastasis (RSLNM) and associated risk factors may guide the selection criteria of level VIIb for inclusion in the target volume for high-precision radiotherapy (RT). However, data clarifying the selection criteria have not yet been established. We evaluated the prevalence of level VIIb RSLNM and associated risk factors in patients with oropharyngeal carcinoma (OPC). <h3>Materials/Methods</h3> Two board-certified radiation oncologists with an experience of 15 and 17 years in diagnosing and treating head and neck cancers retrospectively reviewed pretreatment [<sup>18</sup>F]-fluoro-2-deoxy-D-glucose–positron emission tomography/computed tomography (CT) along with contrast-enhanced thin slice CT and magnetic resonance (MR) images of 137 patients pathologically confirmed as having OPC who underwent RT. Observers independently evaluated the images without prior knowledge regarding the clinical information of the patients, and disagreements were resolved by consensus. The location of LN was confirmed on the planning CT images. In addition to RSLNM assessment, which includes the short-axis diameter and the maximum standardized uptake value (SUV<sub>max</sub>), long-axis diameter of the largest LN in the upper limit of ipsilateral level II (caudal edge of the C1 lateral process) was recorded. Fisher's exact test and logistic regression analyses were made to determine the risk factors of RSLNM. <h3>Results</h3> RSLNM was confirmed in 18 (13%) patients. All RSLNMs were located within level VIIb on the planning CT images. The median short-axis diameter and SUV<sub>max</sub> of RSLNM were 11 mm (range 8–15) and 5.2 (range, 1.9–9.4), respectively. No patients exhibited LNM in contralateral level VIIb. Furthermore, no patients with negative or single ipsilateral cervical LNM had RSLNM. Fisher's exact test revealed that smoking status (p = 0.027), multiple ipsilateral cervical LNM (p = 0.045), and LN ≥ 15 mm in the upper limit of ipsilateral level II (p < 0.001) were significantly associated with RSLNM. Logistic regression analyses revealed that the only factor significantly associated with RSLNM was LN ≥15 mm in the upper limit of ipsilateral level II (odds ratio: 977.297, 95% CI: 57.629–16573.308; p < 0.001). <h3>Conclusion</h3> RSLNM is relatively common in patients with OPC with a prevalence rate of approximately 10%. The prevalence of RSLNM in patients with negative or single ipsilateral cervical LNM and contralateral RSLNM is extremely low; therefore, level VIIb can be excluded from the target volume in such patients. LNs ≥ 15 mm in the upper limit of ipsilateral level II is a risk factor for RSLNM. Ipsilateral level VIIb should be included in the target volume for patients with this risk factor.