In this study, we retrospectively evaluated patients with upper gastrointestinal bleeding (UGB) who were followed up at our center over a 3 year period and aimed to determine the factors affecting mean platelet volume (MPV) in patients with UGB, temporal changes in MPV during UGB, and the relationship between MPV values and the severity of UGB. Patients and methods: A total of 170 patients who were hospitalized between January 2010 and December 2013 with a diagnosis of UGB, completed a 72-hour follow up, and had a baseline blood count performed within 6 months were evaluated retrospectively. Demographic, clinical, and laboratory data, along with MPV values at baseline, on admission, and at 4 hours, 1 day, 2 days, 3 days, and discharge, were evaluated. Number Cruncher Statistical System (NCSS) 2007 was used for statistical analyses. Results: Women and patients with comorbid diseases had higher baseline MPV values; this effect disappeared after admission for UGB and reappeared at discharge. MPV values were lowest at the start of the bleeding and significantly increased during the course of UGB. Baseline MPV and MPV at discharge values were similar. There was no statistically significant relationship between any MPV measurement and transfusion amount. Conclusion: The effects of gender and comorbid diseases were negated by the presence of UGB and returned after UGB was controlled. MPV levels exhibited temporal changes during the course of UGB, indicating that MPV can be used as a marker; however, no statistical relationship was found between temporal MPV values and transfusion amount, a marker for UGB severity.