Description: Objective p53 immunostaining in Barrett's oesophagus has been shown to be predictive of progression but data regarding its generalisability to routine practice are lacking. This study compared the reliability of p53 and dysplasia interpretation and grading.Methods: 72 cases encompassing the full spectrum of BO were circulated to 10 pathologists from 4 institutions after a brief training session in p53 interpretation. Each pathologist classified cases on the H&E alone using the Vienna classification and assessed the p53 staining using a qualitative system. Agreement was assessed using kappa statistics. Results For the 4 tier Vienna system the average unweighted kappa was 0.30 Weighted Kappa values varied from 0.27-0.69 with an average of 0.47. When grouped into definite dysplasia vs no definite dysplasia) the average kappa was 0.55, but the kappa for LGD vs HGD was only 0.31. For p53 using the 3 recognised patterns, the unweighted kappa was 0.6 (CI 0.58-0.63). When cases were evaluated with both H&E and p53 the average kappa was 0.61 for definite dysplasia vs the rest. Conclusion p53 immunohistochemistry interpretation is more reliable than dysplasia diagnosis, even with limited training. As it is predictive of prognosis and improves diagnostic reproducibility, it is suitable for routine use by pathologists as an adjunct to dysplasia diagnosis. The distinction of LGD vs HGD was poor. This study supports simplifying dysplasia diagnosis into “present”, “indefinite” or “absent”, and the use of p53 as an ancillary marker in difficult cases. This should help prevent overdiagnosis of dysplasia and inappropriate treatment. This article is protected by copyright. All rights reserved.