This paper is adapted from: Gross MT: Tendinitis. In: Prentice W, Hooker DN (eds), Postgraduate Advances in Sports Physical Therapy, I-III, pp 1-14. Berryville, VA: Forum Medicum, Inc., 1990. Figures and segments of text in this paper are reprinted with permission of Forum Medicum, Inc. Chronic tendinitis is a common and debilitating musculoskeletal pathology that can be particularly recalcitrant to treatment. Details of the composition and structure of tendon are presented, enabling clinicians to understand the mechanical function of tendon under different loading conditions and the various mechanisms of tendinitis injury. The effects of exercise, disuse, the incidence of injury, and tendinitis terminology are discussed. Other purposes of this paper are to describe the natural course of tendon healing, the clinical assessment of tendinitis, and suggested treatments for chronic tendinitis. The paper concludes with two case studies. Information in this paper should assist the clinician in treating chronic tendinitis more successfully. J Orthop Sports Phys Ther 1992;16(6):248-261.