The patient‐reported outcomes version of the Common Terminology Criteria for Adverse Events (PRO‐CTCAE) complements capture of symptomatic adverse events (AEs) by clinicians. Previous trials have typically used a limited subset of relevant symptomatic AEs to reduce patient burden. We aimed to determine the feasibility of administering all 80 AEs included in the PRO‐CTCAE library by approaching consecutive patients enrolled in a large academic phase I program at three points in time. Here, we report a preplanned analysis after enrolling the first 20 patients. All items were answered on 51 of 56 potential visits (adherence 91%). Three (5%) additional PRO‐CTCAE assessments were partially completed, and two (4%) were missed because of conflicting appointments. No patient withdrew consent or chose not to complete the assessments once enrolled on study. Future trials of experimental drugs that incorporate the PRO‐CTCAE should consider using this unselected approach to identify adverse events more completely. Evidence shows that subjective toxicities are underreported in patients with cancer and that collection of this information directly from patients can improve the reliability and precision of symptomatic adverse events detection. This study reported the feasibility of using the complete set of subjective symptoms from PRO‐CTCAE library developed by the National Cancer Institute in patients on phase I clinical trials.