Background: Twenty-five to 85% of trauma patients are under the influence of alcohol in addition to experiencing injury-related coagulation impairment. Viscoelastic point-of-care tests (thrombelastography [TEG], rotational thromboelastometry [ROTEM]) are popular tools for rapid hemostasis assessment and therapeutic decision-making in this and other settings. While alcohol affects these tests in-vitro, their specific effects in-vivo are unclear. Therefore, we evaluated the effects of alcohol ingestion on ROTEM parameters. Methods: Twenty volunteers provided informed consent to drinking red wine, whisk(e)y, or vodka to a target blood alcohol concentration of 1 ‰ within one hour, calculated with the Widmark formula. Blood samples were collected before drinking, at a breath alcohol concentration of 0.5 ‰, and at 1.0 ‰, but no later than one hour. After each blood collection, ExTEM and FibTEM tests were performed directly "at the bedside." Results: All participants had a blood alcohol concentration (BAC) of 0.00 ‰ at the beginning. The mean BACs at the second and third collection were 0.48 and 0.76 ‰, respectively. There were no significant differences in the ExTEM parameters. FibTEM measurements showed a significant difference at the A10 value (13.0 vs. 14.0 mm, P = 0.014) and a trend at the maximum amplitude (maximum clot firmness [MCF] 13.7 vs. 16.2 mm, P = 0.075). We saw no significant differences in fibrinolysis parameters and no hyperfibrinolysis in our ROTEM measurements. Conclusions Ethanol ingestion can impair early fibrin polymerization. These results might be of special relevance in trauma and support routine application of ROTEM/TEG in such cases.