Palliative care is underutilized, and research has neglected patient-level factors including attitudes that could contribute to avoidance or acceptance of palliative care referrals. This may be due in part to a lack of existing measures for this purpose.To develop and validate a 9-item scale measuring patient attitudes toward palliative care, comprised of 3 subscales spanning emotional, cognitive, and behavioral factors.Data were collected online in three separate waves, targeting individuals with cancer (Sample 1: N=633; Sample 2: N=462) or non-cancer serious illnesses (Sample 3: N=225). Participants were recruited using ResearchMatch.org and postings on the websites, social media pages, and listservs of international health organizations.Internal consistency was acceptable for the total scale (α=.84) and subscales: emotional (α=.84), cognitive (αs=.70), and behavioral (α=.90). The PCAS-9 was significantly associated with a separate measure of palliative care attitudes (ps<.001) and a measure of palliative care knowledge (ps<.004), supporting its construct validity in samples of cancer and non-cancer serious illnesses. The scale's psychometric properties, including internal consistency and factor structure, generalized across patient subgroups based on diagnosis, other health characteristics, and demographics.Findings support the overall reliability, validity, and generalizability of the PCAS-9 in serious illness samples and have implications for increasing palliative care utilization via clinical care and future research efforts.