Effective documentation serves as a cornerstone for communication and patient care, especially in radiation oncology (RO). Studies have shown room for improvement in documentation practices, and although documentation guidelines exist, it is uncertain if RO physicians are aware of or adhere to them. We aimed to assess RO resident physicians' medicolegal knowledge and the impact of an educational intervention on documentation practices. Grading rubrics for consultation and progress notes were created using guidelines, comprising of a fundamental score and total score. Residents from two institutions attended a didactic seminar on medicolegal documentation. Pre- and post-seminar, an electronic anonymous survey was used to assess resident knowledge and perspectives and random resident consultation and progress notes were scored. Mean documentation and survey item scores from pre- and post-seminar were compared. Fourteen resident physicians participated and completed surveys, and 48 consultation notes and 40 progress notes were analyzed. No participant had prior education specific to RO documentation, nor were any aware of available resources. Post-seminar, participants' medicolegal documentation knowledge significantly increased (86.61% vs. 95.54%, p = 0.001), as did the fundamental score (83.64% vs 89.29%, p = 0.041) and total scores of consultation notes (69.82% vs. 78.98%, p = 0.001) and total score of progress notes (55% vs. 75.19%, p < 0.001). Our seminar significantly enhanced residents' medicolegal knowledge and quality of documentation, and surveys revealed a lack of speciality specific documentation education. This combined with findings from other studies and participant opinions suggest that resident physicians would benefit from such training during residency.