Background: There are no agreed national nor international criteria for referral to palliative care. Key population characteristics have been defined to aid the generalizability of research findings in palliative care clinical studies. To codify differences in key demographic factors between patients with cancer participating in the Australian national Cancer Supportive Care Clinical Studies Collaborative (CSCCSC) phase III symptom control studies and the population referred to other Australian palliative care services. Methods: This study compares two contemporaneous consecutive cohorts generated through clinical trial participation and the national palliative care clinical quality improvement registry in Australia. Age, sex, cancer diagnosis, language, and socio-economic status were compared. Results: Cohorts were people with cancer: enrolled in CSCCSC phase III clinical studies (n=902; 17 sites); and registered by the Australian national Palliative Care Outcomes Collaboration (PCOC; n=75,240; 117 sites). Participants in CSCCSC studies were younger than those of PCOC (median 71 (IQR 62, 79) versus median 73 (IQR 63, 81); p=0.003 respectively). There was no significant difference in sex (p=0.483). Patients who spoke English accounted 95.0% of enrollees in the CSCCSC group and 92.2% in the PCOC group (p = 0.004). Clinical study participants had higher socioeconomic status that the PCOC group (p=0.022). Conclusions: Overall, the slightly different demographic patterns are reflective of the differences often seen between phase III trials and the populations to whom the results will be applied. Age differences particularly need to be taken into account when considering the best way to apply each study’s findings.