Tendonopathy, resulting in the loss of mechanical strength of a tendon, is a serious health problem affecting many people. The common symptom of tendonopathy is pain – patients' daily activities, their participation in sport and exercise, and their ability to work are greatly compromised. Tendonopathy is considered to be a degenerative disorder caused by repetitive injury of the tendon. The most common tendon lesions are Achilles tendon rupture, lateral epicondylitis (tennis elbow) and rotator cuff tear. However, in spite of its clinical significance, our knowledge about tendonopathy is still very poor. This research was undertaken to investigate the pathology of tendonopathy. It is proposed that apoptosis, autophagic cell death and myofibroblasts play a role in the progression of tendonopathy in the rotator cuff; the aim of this study was therefore to determine if this was indeed the case. Tendon tissues were collected from 30 patients suffering from rotator cuff tears. A terminal deoxynucleotidyl transferase biotin-dUTP nick end labelling (TUNEL assay) was performed to detect apoptosis. Autophagic cell death of the tenocytes in the ruptured rotator cuff tendon was detected by immunohistochemical staining for ubiquitin. Myofibroblasts were identified immunohistochemically with anti-alpha-smooth muscle actin (anti--SMA) antibody. The distribution of apoptosis, autophagic cell death and myofibroblasts, as well as the total cell density, were assessed respectively and were correlated using a four-category (i.e. graded from 0-3) degeneration of collagen matrix. – 6 – The results showed that apoptosis, autophagic cell death and myofibroblasts were observed in all of the samples. The highest percentage of autophagic cell death was evidenced in the Grade 2 matrix, while the percentage of apoptosis increased significantly with the increase of matrix degeneration from Grade 0-3; a similar pattern was found for myofibroblasts. The total cell numbers varied among the matrix grades, with the maximum and minimum percentages occurring in Grades 1 and 3, respectively. It can be concluded that apoptosis, autophagic cell death and myofibroblasts might be closely related to the damage of the extracellular matrix (ECM) structure.