Urinary catheterization is a complex procedure. Traditional teaching in classroom, such as using a simulator, is not enough to guarantee the necessary learning outcomes. It is therefore necessary to implement new active learning approaches such as the flipped classroom. The aim of this study was to examine the effect of the use of the flipped classroom on the level of self-efficacy and the assessment of clinical competencies in nursing students performing the urinary catheterization procedure. A quasi-experimental study of a single group with pre-/post-testing measures. A convenience sample of 139 nursing students. A flipped classroom approach was implemented. Measurements were taken pre and post intervention. This study followed the consolidated criteria for quality of nonrandomized evaluations studies (TREND) checklist. Regarding self-efficacy, statistically significant differences were found between the pre-test and post-test (Z = −14.453; p < 0.05). With respect to knowledge level, statistically significant differences were found when comparing pre-/post-test results (Z = −14,480; p < 0.05). Furthermore, statistically significant differences were found on the ability scale depending on pre-/post-test (Z = −10.277; p < 0.005); in all cases, obtaining a higher score in the post-test. The flipped classroom could be an effective educational tool for the development of clinical skills, specifically urinary catheterization. This method has been shown to improve the knowledge, skills, and self-efficacy in urinary catheterization of nursing students.