Nonsense-mediated decay (NMD) degrades mRNA containing premature translation termination codons. In yeast, NMD substrates are decapped and digested exonucleolytically from the 5' end. Despite the requirement for translation in recognition, degradation of nonsense-containing mRNA is considered to occur in ribosome-free cytoplasmic P bodies. We show decapped nonsense-containing mRNA associate with polyribosomes, indicating that recognition and degradation are tightly coupled and that polyribosomes are major sites for degradation of aberrant mRNAs.