Objective: Evidence to support the use of pro re nata (PRN) medication is limited, and the details of PRN use (indication, frequency of administration, patient characteristics) are rarely reported, particularly in youth populations. The goal of this study was to report on the pattern of PRN use over 6 years in an acute care psychiatric unit for adolescents. Methods: A retrospective chart review of patients' records from November 2012 to October 2018 was conducted. Variables extracted from electronic medical records included age, gender, race/ethnicity, clinical rating scores at admission (on a subset of patients), length of stay, psychotropic and nonpsychotropic PRN medication administration, timing of administration, discharge diagnosis, and discharge medication. Results: Records from 2961 individuals with a total 3937 admissions were analyzed. A total of 62% of admissions had at least one PRN medication administration. Severity of symptoms, as indicated by higher scores on clinical rating scales at admission, longer length of stay, and readmission were related to high PRN use. Patients with bipolar spectrum disorders received more psychotropic and nonpsychotropic PRN medications than other patients. Patients who were high psychotropic PRN users were also high nonpsychotropic PRN users. Conclusion: Despite the lack of clear evidence in support of the efficacy of PRN medications, they commonly used to control symptoms in acute care inpatient settings. Youth with severe symptoms utilized not only psychotropic PRN medication but also nonpsychotropic PRN more frequently, suggesting a possible role of systemic disorder among youth with serious mental illness. More research is necessary to examine the efficacy of PRN medications for managing targeted symptoms.