Background: This study reports on the analysis of the application and diagnostic predictability of the revised 2014 ICBD criteria in an unselected cohort of UK patients, and the ensuing organ associations and patterns of disease. Methods: A retrospective cohort study was conducted using a database of electronic medical records. Three categories were recognised: clinically defined BD, incomplete BD and rejected diagnoses of BD. We applied the ISG 1990 and ICBD 2014 classification criteria to these subgroups to validate diagnostic accuracy against the multidisciplinary assessment. Results: Between 2012 and 2015, 281 patients underwent initial assessment at an urban tertiary care centre: 190 patients with a confirmed diagnosis of BD, 7 with an incomplete diagnosis, and 84 with a rejected diagnosis. ICBD 2014 demonstrated an estimated sensitivity of 97.89% (95% CI: 94.70 to 99.42) and positive likelihood ratio of 1.21 (1.10 to 1.28). The strongest independent predictors were: Central nervous lesions (OR = 10.57, 95% CI: 1.34 to 83.30); Genital ulceration (OR = 9.05, 95% CI: 3.35 to 24.47); Erythema nodosum (OR = 6.59, 95% CI: 2.35 to 18. 51); Retinal vasculitis (OR = 6.25, 95% CI: 1.47 to 26.60); Anterior uveitis (OR = 6.16, 95% CI: 2.37 to 16.02); Posterior uveitis (OR = 4.82, 95% CI: 1.25 to 18.59). Conclusions: The ICBD 2014 criteria were more sensitive at picking up cases than ISG 1990 using the multidisciplinary assessment as the gold standard. ICBD may over-diagnose BD in a UK population. Patients who have an incomplete form of BD represent a distinct group that should not be given an early diagnostic label. Behcet's disease is a complex disease that is best diagnosed by multidisciplinary clinical assessment. Patients in the UK differ in their clinical presentation and genetic susceptibility from the original descriptions. This study also highlights an incomplete group of Behcet's patients that are less well defined by their clinical presentation.