Objectives. Rheumatoid arthritis is a chronic inflammatory disease with a clinical picture of arthritis, muscle hypotrophy, loss of range of motion, loss of strength and disability. The objective of this study was to evaluate knees of patients with rheumatoid arthritis using an isokinetic dynamometer. Methods. Fifty patients with a diagnosis of rheumatoid arthritis and 50 control subjects were evaluated using an isokinetic dynamometer (Cybex 6.000) regarding the following parameters: peak torque, peak torque angle, power, total work, peak torque acceleration time, set total work, torque acceleration energy ('explosion') and endurance. Comparisons between rheumatoid arthritis and the control group, left side versus right side, flexors and extensors and the proportion between flexors and extensors were made. The subjects were also evaluated through the Health Assessment Questionnaire, visual and analogical scale of pain, EPM-ROM and goniometry of the knee. Results. The results showed that patients with rheumatoid arthritis have less strength than the control group (P < 0.05); the extensors are stronger than the flexors (P < 0.05); no significant differences between the right and the left knee for rheumatoid arthritis and the control group were observed and the proportion between flexors and extensors is the same in both groups. We concluded that regarding the isokinetic parameters, the knees of subjects with rheumatoid arthritis are different from normal knees with decreased strength parameters, maintaining the proportion between flexors and extensors with a global loss of strength in the segment, excluding the high speeds in some of the parameters.