Background: Anaphylaxis is a life-threating hypersensitivity reaction. Epinephrine underuse in patients with anaphylaxis could lead to poor outcomes. There is evidence that the epinephrine use in such patients could be as low as 8%. Objective: To assess the percentage of physicians who know that epinephrine is the first-line treatment in anaphylaxis. The secondary objective was to assess knowledge gaps regarding anaphylaxis diagnosis and treatment that could lead to epinephrine underuse. Methods: We performed an online survey for physicians in Mexico City, using a 10-item questionnaire assessing anaphylaxis knowledge. We obtained measures of central tendency for statistical analysis, such as frequency, 95% confidence interval, as well as the chi-square test for comparing the groups. Results: A total of 196 surveys were considered for analysis. Of all the participants, 96.44% were able to correctly diagnose an anaphylaxis case with cutaneous, respiratory, and cardiovascular symptoms. Fifty-two percent correctly diagnosed anaphylaxis without cutaneous symptoms. The 72.4% of the respondents chose epinephrine as the first-line treatment, 42.3% correctly answered that there is no absolute contraindication to giving epinephrine, and 20.9% ignored whether there was any contraindication for its use. Only 38.3% of participants answered that during discharge they would prescribe an autoinjector. Regarding the administration route, 63.4% answered that the first dose of epinephrine is applied intramuscularly and 50% of the participants chose the correct dose of epinephrine. Only 2.6% of the participants answered all 10 questions correctly. Conclusion: There is still some difficulty recognizing anaphylaxis without cutaneous symptoms. Even though two-thirds of physicians identified that epinephrine is the treatment of choice, only 49.5% would have used intramuscular epinephrine as first-line treatment. We found a low percentage of epinephrine ampule prescription and knowledge of the correct dose. These findings can account for epinephrine underuse when dealing with anaphylaxis in the real clinical practice.