Background: For people on peritoneal dialysis (PD), constipation is associated with technique failure. For those on haemodialysis (HD), constipation has been associated with a reduction in quality of life. Objectives: The objectives of this study were to (i) determine the prevalence of functional constipation; (ii) compare patient perception of constipation with Rome III criteria for functional constipation; (iii) describe the prevalence of constipation and stool form using Bristol Stool Form Scale (BSFS); (iv) determine differences in bowel habit and stool form between those on dialysis compared to pre-dialysis; and (v) determine the diagnostic accuracy of self-perception and the Rome III criteria against the BSFS. A cross-sectional group of pre-dialysis (eGFR < 15 ml/min) and dialysis patients were recruited. A total of 148 patients participated (98 HD, 21 PD and 21 pre-dialysis). Participants: completed a questionnaire consisting of self-perception of the presence of constipation, simplified questions from the Rome III criteria for functional constipation, scored their stool form using the BSFS and reported laxative use. Results: The prevalence of constipation using the Rome III criteria was 12.3%; patient perception 46.3% and 25.7% using the BSFS. Prevalence differed according to the tool used. Conclusion: No single method alone is sufficient for accurately determining if a patient is constipated. Relying on patients’ self-perception may be unreliable. Ideally patient assessment of constipation should incorporate both the Rome III criteria and BSFS in a method such as the one designed as a result of this research. Further research is needed to assess its usability and practicality in clinical practice.