Context: Advances in the management of constipation in palliative care remain hindered by the lack of agreed-upon diagnostic criteria. Objectives: The objective of this work was to emphasize this issue by systematically examining the eligibility and primary outcome measures in studies of constipation in the hospice and palliative care population. Methods: A palliative care-specific electronic literature search was undertaken using the validated domain filter "palliative care" and topic filter "constipation" in CareSearch (www.caresearch.com.au), which interrogates PubMed in real time (1965-2011). Studies were included if they were primary reports of the treatment of constipation in a palliative care setting. Articles could be prospective or retrospective; randomized controlled trials, cohort studies, or case series. Results: Twenty articles on the palliative care population were included in which there were six different definitions of constipation. Only 12 of 20 articles used their cited definitions of constipation as the studies' primary outcome measures and four of four blinded, randomized, controlled trials. Articles that used the time between bowel actions or the use of laxatives as the definition of constipation were most likely to report outcomes based on these criteria. Conclusion: Constipation is a significant problem in palliative care; however, not having an agreed-upon definition limits research initiatives and the ability to apply these results clinically to people with constipation. Four domains are suggested as pivotal to the diagnosis: any life-long history of constipation (using the Rome Criteria), evaluation of physical changes that may cause or worsen constipation, the subjective sensation (such as feelings of incomplete defecation or bloating or fullness), and objective changes (such as frequency or consistency of stools). �� 2013 U.S. Cancer Pain Relief Committee. Published by Elsevier Inc. All rights reserved.