Recent efforts have revealed that numerous protein-coding messenger RNAs have natural antisense transcript partners, most of which seem to be noncoding RNAs. Here we identify a conserved noncoding antisense transcript for β-secretase-1 (BACE1), a crucial enzyme in Alzheimer's disease pathophysiology. The BACE1-antisense transcript (BACE1-AS) regulates BACE1 mRNA and subsequently BACE1 protein expression in vitro and in vivo. Upon exposure to various cell stressors including amyloid-β 1–42 (Aβ 1–42), expression of BACE1-AS becomes elevated, increasing BACE1 mRNA stability and generating additional Aβ 1–42 through a post-transcriptional feed-forward mechanism. BACE1-AS concentrations were elevated in subjects with Alzheimer's disease and in amyloid precursor protein transgenic mice. These data show that BACE1 mRNA expression is under the control of a regulatory noncoding RNA that may drive Alzheimer's disease–associated pathophysiology. In summary, we report that a long noncoding RNA is directly implicated in the increased abundance of Aβ 1–42 in Alzheimer's disease.