Background: Behcet's disease (BD) is an idiopathic, multisystemic, progressive disease. The purpose of this study is to compare the knee flexor and extensor isokinetic muscle strengths of Behcet's patients with that of healthy subjects. Methods: Twenty-five (13 male and 12 female) patients with BD and 25 (15 male and 10 female) healthy individuals were included in the study Velocities of 90 degrees/sec, 120 degrees/sec, and 150 degrees/sec were used for the isokinetic muscle strength testing. Patients with active inflammatory knee arthritis were excluded. Peak torque (Nm) and peak torque adjusted to body weight (%) were taken into consideration for comparison between study groups. Results: Compared to healthy controls, there was a statistically significant decrease in both the bilateral knee extensor and flexor muscle isokinetic peak torques (Nm) as well as the peak torques adjusted to body weight (%) at velocities of 90 degrees/sec, 120 degrees/sec and 150 degrees/sec in patients with BD (p < 0.05). However, there was no significant difference in the agonist-antagonist ratio of the isokinetic peak torques of knee muscles between the two groups. Conclusion: In light of these findings, we have concluded that both knee flexor and extensor isokinetic muscle strengths are lower in BD. We therefore recommend careful monitoring of patients with BD in temis of muscle strength.