Updated project metadata. Aspirin, or acetylsalicylic acid is widely used to control pain, inflammation and fever. Important to this function is its ability to irreversibly acetylate cyclooxygenases at active site serines. Aspirin has the potential to acetylate other amino-acid side-chains, leading to speculation that aspirin-mediated lysine acetylation could explain some of its drug actions or side-effects. Using a labeled form of aspirin, aspirin-d3, we identified over 12000 sites of lysine acetylation from cultured human cells. Although aspirin amplifies acetylation signals at thousands of sites, cells tolerate aspirin mediated acetylation very well unless endogenous deacetylases are inhibited. Apart from a limited number of cellular proteins that are substantially acetylated under endogenous conditions, aspirin mediated acetylation leads to a large increase in the acetylation of many proteins even although they remain at very low stoichiometry. This reinforces the idea that a major function of cellular deacetylases is the suppression of non-specific or non-enzymatic protein acetylation.