Background: Locally advanced HNSCC is treated curatively, but recurrence is common. In HNSCC, EGFR is richly expressed and EGFR inhibition is validated treatment (tx); the ErbB family blocker afatinib (A) showed efficacy in recurrent/metastatic disease. This Phase III trial assessed if A after definitive CRT improves disease-free survival (DFS). Methods: Eligible pts had complete response after CRT ≥66 Gy (or equivalent) with concurrent cisplatin or carboplatin but not prior EGFR inhibition, for HNSCC of oral cavity, hypopharynx, larynx, or oropharynx with >10 pack years (pk yrs) tobacco use. Pts were stratified by ECOG PS (0/1) and nodal stage (N0–2a/N2b–3), and randomized 2:1 to A 40 mg/d or placebo (P); tx continued for 18 m if tolerated, or until disease recurrence. The primary endpoint was DFS. Results: Of 669 pts planned, 617 were randomized; A 411, P 206. Median age was 58 yrs; 86% were male; 65% ECOG PS 0; most had smoked (A/P ex-smoker: 66/72%; current: 28/22%). Subsites (A/P) were: oropharynx 53/54%; hypopharynx 21/23%; larynx 18/12%; oral cavity 9/10%. The majority had T3 or 4 (A/P 70/68%) and N2 disease (67/63%). Accrual was halted for futility on independent DMC recommendation: at a pre-planned interim analysis (40% of DFS events), median DFS was A 43.4 m vs P not reached (NR; HR 1.13 [95% CI 0.81–1.57], p=0.48); the Table shows key subgroups. Median treatment duration was A 300.0 d, P 455.5 d. Recurrence was A 23%, P 23%. Dose reduction of A was required in 53% (mostly due to diarrhea, stomatitis). Tx was discontinued due to AEs in A 15%, P 4%. Conclusions: A after CRT did not improve DFS vs P. Subgroup analyses were underpowered to provide definitive conclusions. Harrington and Cohen contributed equally. Clinical trial information: NCT01345669