Abstract: Introduction: Behcet's disease (BD) is characterized by recurrent attacks followed by remissions, making difficult the assessment of a given treatment. The aim of this study was to compare the Iran Behcet's Disease Dynamic Activity Measure (IBDDAM) with the physician's global assessment (PGA) in evaluating the treatment result. Materials & Methods: Ninety-six patients with BD were followed prospectively, regardless of their treatment modality. The range of follow up was 3 to 62 months with a mean of 14.3 + 15.3 months. The change in the IBDDAM was compared with the PGA. Results: The PGA showed no change in the disease activity in 62 patients during the study. In this group the IBDDAM of 49 patients (79%) remained unchanged; it increased in 7 (11%) and decreased in 6 (10%) of them. According to their disease activity two subgroups were characterized: 1- Twenty-four had an active disease; lBDDAM did not change in 16 (67%), improved in 5 (21%) and aggravated in 3 (12%). 2- In 38 patients the disease was in remission; IBDDAM was stable in 33 (87%), improved in 1 (3%) and aggravated in 4 (10%) patients. The difference between the 2 subgroups was statistically significant (X 2=4.933, p<0.03). In 9 patients the PGA showed a disease aggravation; the IBDDAM also increased in them. In 25 patients the PGA showed an improvement; in 23 of them (92%) the IBDDAM improved and in the other 2 (8%) patients it remained constant. In overall the IBDDAM changes were in agreement with the disease evolution determined by the PGA in 84% of the cases (the confidence interval at 95% was 7.3). Conclusion: IBDDAM can be a reliable index to evaluate the response of BD patients to the treatment. The overall sensitivity is 84%. The sensitivity increases when the disease activity changes (improves or aggravates).