Objective: Self-medication is a common practice among university students worldwide. It is also common among medical students and has been associated, in the case of non-steroid, antiinflamatory drugs, with renal, cardiovascular, and gastrointestinal adverse effects and multidrug-resistance in the case of antibiotics. The objective of this study was to determine the prevalence of self-medication with antibiotics and analgesics in undergraduate medical students and to characterize the attitudes, knowledge, and practices related to this behavior. Methodology: Cross-sectional study. 625 undergraduate medical students from a private university in Medellin, Colombia participated. A 45-question survey was designed. The dependent variable was self-medication of antibiotics and analgesics. Proportions and means with their dispersion measurements were obtained. We explored possible associations between the practice of self-medication, gender, and the training semester. Significant value was taken as p <0.05. Results: The survey was taken by 625 undergraduate medical students, that is, 58% of all students. Of these, 67% were women. The female to male ratio was 2:1. The median age was 20 years (interquartile range: 3). The prevalence of self-medication with analgesics was 84% for women and 81% for men, while with antibiotics it was 28% for women and 21% for men. 90.1% of students expressed that practicing self-medication was unsafe; likewise, 93% of students recognized that self-medication with antibiotics produces antimicrobial resistance. Regardless, 78.6% said they would continue to self-treat. Discussion: Self-medication with analgesics and antibiotics is a common and complex behavior in undergraduate medical students. While they are aware of the risks involved in this practice, most are not willing to change it.