OBJECTIVE: Visual timelines of patient-reported outcomes (PRO) can help prostate cancer survivors manage longitudinal data, compare with population averages, and consider future trajectories. PRO visualizations are most effective when designed with deliberate consideration of users. Yet, graph literacy is often overlooked as a design constraint, particularly when users with limited graph literacy are not engaged in their development. We conducted user testing to assess comprehension, utility, and preference of longitudinal PRO visualizations designed for prostate cancer survivors with limited literacy. MATERIALS AND METHODS: Building upon our prior work co-designing longitudinal PRO visualizations with survivors, we engaged 18 prostate cancer survivors in a user study to assess 4 prototypes: Meter, Words, Comic, and Emoji. During remote sessions, we collected data on prototype comprehension (gist and verbatim), utility, and preference. RESULTS: Participants were aged 61-77 (M = 69), of whom half were African American. The majority of participants had less than a college degree (95%), had inadequate health literacy (78%), and low graph literacy (89%). Among the 4 prototypes, Meter had the best gist comprehension and was preferred. Emoji was also preferred, had the highest verbatim comprehension, and highest rated utility, including helpfulness, confidence, and satisfaction. Meter and Words both rated mid-range for utility, and Words scored lower than Emoji and Meter for comprehension. Comic had the poorest comprehension, lowest utility, and was least preferred. DISCUSSION: Findings identify design considerations for PRO visualizations, contributing to the knowledge base for visualization best practices. We describe our process to meaningfully engage patients from diverse and hard-to-reach groups for remote user testing, an important endeavor for health equity in biomedical informatics. CONCLUSION: Graph literacy is an important design consideration for PRO visualizations. Biomedical informatics researchers should be intentional in understanding user needs by involving diverse and representative individuals during development.