e21534 Background: Phase I clinical trials (P1Ts) are an essential step in the validation of novel therapies to treat childhood cancer. Children with cancer participate in P1Ts when no known curative therapy remains for their cancer. It is important to understand the experiences of children with advanced cancer and their families in P1Ts to ensure that participation supports the participants well-being. Methods: An empirical phenomenology study, using an adapted Colaizzi method, was conducted of 11 parents lived experiences of their childs participation in pediatric oncology P1Ts. Parents were recruited from two pediatric academic medical centers in the Midwest United States and from national childhood cancer groups not affiliated with either medical center. Parents participated in individual interviews (mean length 59.1 minutes), with one broad data-generating question. Demographics and the childs clinical trial records provided additional context for understanding the experiences. This presentation describes the study themes identified that were specifically related to pediatric oncology P1T processes and logistics. Results: Parents experiences during the P1Ts were primarily positive. However, data analysis revealed five aspects of P1T participation that were problematic for parents to varying degrees. These aspects were: (1) Learning About Clinical Trials, (2) Being Referred to Another Institution, (3) Undergoing Research-Only Procedures, (4) Complying with the Trial Requirements, and (5) Taking Oral Medications. Conclusions: While overall experiences during P1T participation were positive, improvements can be made that could potentially enhance participants experiences. In particular, enhancing the education provided to participants during on-trial processes and minimizing the logistical burdens associated with P1T requirements may help to address problematic aspects of P1Ts.