Patient online access to medical records can foster patient empowerment and advance patient-centered healthcare. Despite high patient interest, user rates often remain low. While previous research has identified determinants influencing the adoption of online access, this study assessed the relevance of these determinants. By doing so, this study aimed to point towards measures to improve adoption efficiently. Further, supporting patient informed decision-making about using online access might facilitate sustained use. Therefore, conducting a nationwide online survey study among Dutch adults, we examined the relevance of twenty-two psychological determinants for use of online access (N=1888) and decisional conflict (as an indicator of uninformed decision-making) regarding use (N=3403). Analyses concerned visualization of univariate distributions of determinants and their associations with 1) use and 2) decisional conflict regarding use. Greater relevance was indicated by lower means and stronger associations. Results showed that secured data privacy and feeling sufficiently instructed were most relevant for use. Concerning decisional conflict regarding use, additionally, patients’ beliefs about the effects of online access on their ability to participate in their healthcare process and on the patient-provider-relationship were most relevant. Overall explained variance was low (R2=.17 for use and R2=.19 for decisional conflict).Efficiently supporting the use of online access and informed decision-making about use might be achieved by addressing data privacy, providing clear instructions, and communicating potential effects. The low explained variance indicates the need for additional measures, such as facilitating easy opportunities and understanding individual patient preferences.