The objective of this study was to evaluate the effectiveness of eccentric strengthening. Ninety-four subjects (50 men) with chronic lateral epicondylitis were allocated randomly into three groups: stretching, concentric strengthening with stretching, and eccentric strengthening with stretching. Subjects performed an exercise program for six weeks. All three groups received instruction on icing, stretching, and avoidance of aggravating activities. The strengthening groups received instruction on isolated concentric and eccentric wrist extensor strengthening, respectively. At six weeks, significant gains were made in all three groups as assessed with pain-free grip strength, Patient-rated Forearm Evaluation Questionnaire, Disabilities of the Arm, Shoulder, and Hand questionnaire, Short Form 36, and visual analog pain scale. No significant differences in outcome measures were noted among the three groups. Although there were no significant differences in outcome among the groups, eccentric strengthening did not cause subjects to worsen. Further studies are needed to assess the unique effects of a more intense or longer eccentric strengthening program for patients with lateral epicondylitis.