Pre-exposure prophylaxis (PrEP) is a lifesaving medical intervention that protects against human immunodeficiency virus (HIV), but to date, PrEP uptake has been limited. PrEP utilization and adherence among youth, including stigmatized and highly vulnerable young sexual and gender minorities, have been exceptionally low across all regions, leading to preventable HIV transmission. Considering the scientific value of measuring and understanding predictors or associations of PrEP adherence, our study team validated two scales: a PrEP Difficulties Scale and a PrEP Confidence Scale tested within the Adolescent Trials Network P3 study (2019-2021). Data from sexual and gender minorities who were prescribed PrEP across nine domestic sites were evaluated ( = 235). Descriptive statistics, exploratory factor analysis, and correlation coefficients are reported herein. Results for the PrEP Difficulties Scale yielded a four-factor solution (Disclosure, Health Effects, Logistics, and Cost), and results for the PrEP Confidence Scale produced a three-factor solution (Scheduling, Distraction, and Planning). Factor loadings and Cronbach's alphas suggested good internal consistency for both scales. PrEP Confidence Scale subscales were correlated with PrEP adherence, and subscales of both scales were associated with dimensions of social support and PrEP-related stigma. Given the persistence of preventable HIV infections among key populations, multi-level barriers and facilitators to medication adherence, and expansion of PrEP modalities, the PrEP Difficulties Scale and PrEP Confidence Scale have the potential to enhance intervention, exploratory, and mechanistic HIV prevention research. ClinicalTrials.gov Identifier: NCT03320512.