A germline mutation in the 3′-untranslated region of KRAS (rs61764370, KRAS-variant: TG/GG) has previously been associated with altered patient outcome and drug resistance/sensitivity in various cancers. We examined the prognostic and predictive significance of this variant in recurrent/metastatic (R/M) head and neck squamous cell carcinoma (HNSCC). We conducted a retrospective study of 103 HNSCCs collected from three completed clinical trials. KRAS-variant genotyping was conducted for these samples and 8 HNSCC cell lines. p16 expression was determined in a subset of 26 oropharynx tumors by immunohistochemistry. Microarray analysis was also utilized to elucidate differentially expressed genes between KRAS-variant and non-variant tumors. Drug sensitivity in cell lines was evaluated to confirm clinical findings. KRAS-variant status was determined in 95/103 (92%) of the HNSCC tumor samples and the allelic frequency of TG/GG was 32% (30/95). Three of the HNSCC cell lines (3/8) studied had the KRAS-variant. No association between KRAS-variant status and p16 expression was observed in the oropharynx subset (Fisher's exact test, P = 1.0). With respect to patient outcome, patients with the KRAS-variant had poor progression-free survival when treated with cisplatin (log-rank P = 0.002). Conversely, KRAS-variant patients appeared to experience some improvement in disease control when cetuximab was added to their platinum-based regimen (log-rank P = 0.04). The TG/GG rs61764370 KRAS-variant is a potential predictive biomarker for poor platinum response in R/M HNSCC patients. NCT00503997, NCT00425750, NCT00003809.