To define the association of the ingestion of nonsteroidal anti-inflammatory drugs (NSAIDs), including aspirin (ASA), and lower gastrointestinal bleeding (GIB) a retrospective, case-controlled study was undertaken of 188 patients admitted to three community hospitals in three cities with a diagnosis of lower GIB. Information was obtained about NSAID usage among these patients, and the data were compared with an age- and sex-matched control group of 185 patients admitted with a nongastrointestinal diagnosis, derived from a daily admission list. At the time of admission, in the New Jersey group, NSAID consumption was present in 26 of 90 (29%) patients with lower GIB compared with 16 of 90 (18%) of controls (P < 0.05, odds ratio 1.88, 95% CI 1.2-3.1) whereas, in the South Carolina group 34 of 98 (35%) were taking NSAID compared with 18 of 95 (19%) of controls (P < 0.01, odds ratio 2.27, 95% CI 1.2-4.4). These data indicate that there is a significantly increased rate of NSAID ingestion in patients admitted with lower GIB, implying that NSAID may unmask bleeding from a variety of lower gastrointestinal lesions.