Little is known about why physicians prescribe inappropriate stress ulcer prophylaxis (SUP) among nonintensive care unit (ICU) hospitalized patients without supporting evidence. This study seeks to understand which factors influence physician prescribing behavior regarding SUP. We designed a cross sectional web-based survey to assess physicians' knowledge, beliefs, and behavior surrounding the prescribing of SUP for non-ICU patients. The survey was emailed to internal medicine residents and hospitalists at a university-affiliated tertiary care hospital. Clinically relevant bivariable associations were examined in logistic regression to determine whether these associations remained after adjustment for potential confounding factors. Sixty-nine percent of physicians reported prescribing SUP to ≥25% of patients. In multivariable analyses, the following factors were associated with higher level of prescribing (≥25%) of SUP: fear of gastrointestinal bleeding (OR = 2.7, 95% CI 1.07, 7.28) and of the legal repercussions of not prescribing SUP (OR = 3.02, 95% CI 1.07, 8.56), whereas knowledge of SUP indications (OR = 0.39, 95% CI 0.20, 0.74) and concern about side effects (OR = 0.24, 95% CI 0.09, 0.61) were associated with low prescribing behavior. Level of training was not associated with prescribing rate. Less than half of respondents were able to identify a single side effect of proton pump inhibitor therapy. Fear of legal repercussions and ignorance of the side effects of acid suppressive therapy were strongly associated with inappropriate prescribing of SUP. Educating physicians about the adverse effects of acid suppression therapy and about existing national guidelines might reduce inappropriate prescribing.