Purpose: The prognosis of head and neck squamous cell carcinomas (HNSCC) remains disappointing and the development of novel anti-cancer agents is urgently awaited. We identified by a functional genetic screen microRNAs that are selectively lethal for head and neck cancer cells but not for normal cells. We further investigated the genes targeted by these microRNAs. Experimental Design: A retroviral expression library of human microRNAs was introduced in HNSCC cell lines and normal oropharyngeal keratinocytes to identify tumor-selective lethal microRNAs. Potential downstream gene targets of these microRNAs were identified by gene expression profiling and validated by functional assays. Results: We identified six microRNAs that selectively inhibit proliferation of head and neck cancer cells. By gene expression profiling and 30-untranslated region (UTR) luciferase reporter assays, we showed that the ataxia telangiectasia mutated (ATM) gene is a common target for at least two and likely three of these microRNAs. Specific inhibition of ATM resulted in a similar tumor-specific lethal effect, whereas the phenotype was reverted in rescue experiments. Conclusions: These six microRNAsmight be developed as novel anti-cancer agents and highlight ATMas an interesting novel therapeutic target for head and neck cancer. © 2013 AACR.