© 2017 Wiley Periodicals, Inc. Background: The Risk Model is a validated prognostic schema for patients with oral cavity squamous carcinoma. Here, we examine the relationship between Worst Pattern of Invasion-type 5 (WPOI-5) and occult cervical metastases, and also present an interim observational analysis of the impact of adjuvant radiotherapy on patients with low-stage oral cancer classified as either high risk or WPOI-5 alone. Methods: There were 323 patients with T1T2cNo oral cavity squamous carcinoma treated by primary resection, 152 of whom also underwent elective neck dissection (END). The resection specimens were examined for worst pattern of invasion, perineural invasion, and lymphocytic host responses, and classified as low risk, intermediate risk, or high risk. Fisher's 2-tailed exact test and Kaplan-Meier outcome analyses were performed. Results: High-risk classification is significantly associated with decreased time to local recurrence (p = .0128; hazard ratio [HR], 2.82; 95% confidence interval [CI], 1.22-6.5) and regional metastasis (p = .052; HR, 3.27; 95% CI, 1.42-7.5). For patients undergoing END, 31 (20%) had occult-positive lymph nodes. WPOI-5 is significantly predictive of occult cervical metastases (p < .0001). We examined the impact of adjuvant radiotherapy on the WPOI-5 subgroup (n = 55). Despite being underpowered, Kaplan-Meier curves demonstrate good separation between patients with low-stage WPOI-5 who received postoperative adjuvant radiotherapy versus those treated by surgery alone, with respect to disease-specific mortality and disease-free survival. Conclusion: WPOI-5 is significantly predictive of occult metastatic disease in cervical lymph nodes. Interim analysis of patients with low-stage WPOI-5 for the impact of adjuvant radiotherapy justifies continuing patient accrual in an observational setting. These data can ultimately support a clinical trial for more aggressive treatment in this niche group.