Abstract: INTRODUCTION: The pathergy phenomenon (PP) is one of the hallmarks of Behcet's Disease (BD). It has been reported to be positive from 17.5% to 83% of cases in different studies. PP is used as a diagnosis criterion in the Dilsen criteria, the Japan criteria, the International criteria, and the Iran criteria. It is therefore important to know whether PP is a fix manifestation of the disease or a cyclic manifestation like mucocutaneous disorders. MATERIALS AND METHODS: To evaluate the characteristic of PP over a period of time, 77 patients were selected randomly (regardless of their disease activity or their disease manifestations), to have a second pathergy test. The pathergy test was performed by needle puncture on the skin of the forearm. 3 methods were used: 1- Needle prick with a 21 gauge needle. 2- Needle prick with a 25 gauge needle. 3- Needle prick with a 25 gauge needle and the injection of 1 drop of a sterile normal saline solution. The result was evaluated 24 hours later. RESULTS: The shortest interval between two tests was one month and the longest 13 years. The mean interval was 35.4 months. The standard deviation was 36.6. Thirty nine patients had a negative PP at their first evaluation. At the second evaluation 27 remained negative while 12 changed to positive. Thirty eight patients had a positive PP at their first evaluation. At the second evaluation 19 remained positive while 19 changed to negative. Although there is a difference between the two groups, it is not statistically significant (X2 =3.813, p=0.05). CONCLUSION: Our data demonstrates that the pathergy phenomenon in Behcet's Disease is waxing and waning, like the majority of other clinical manifestations. Therefore it may be repeated, if necessary, for diagnosis purposes.