BACKGROUND: Although perineural invasion (PNI) is recognized as an adverse prognostic factor in oral tongue squamous cell carcinoma (SCC), the patterns of failure are poorly defined. METHODS: Patients with oral tongue SCC who received primary surgical treatment were identified. Specimens were reviewed by head and neck pathologists. Disease-specific survival (DSS) and locoregional recurrence-free survival (LRFS), regional recurrence-free survival (RRFS), and distant recurrence-free survival (DRFS) were calculated. The PNI and PNI characteristics were analyzed as predictors of outcome. The utility of grading the extent of PNI was assessed by quantifying the number of PNI foci per slide reviewed, nerve caliber, and percent circumference involved. RESULTS: Patients with PNI had a decreased DSS; however, PNI was not predictive of LRFS or RRFS. Patients with PNI were more likely to develop a distant recurrence and 19.40 (confidence interval [CI] 6.70-56.14; P < .001) times more likely to develop a distant recurrence if PNI foci density was >1. CONCLUSION: The presence of PNI in oral tongue SCC predicts worse DSS, with distant recurrence as the most common pattern of failure. High PNI foci density is associated with worse DRFS.