This case study discusses the possible relationship between chronic Achilles tendinitis and sacroiliac joint dysfunction. The patient presented is an active pole jumper, competing at both the national and international levels. He suffered from chronic Achilles tendinitis during the 1994-95 season, and conservative treatment applied locally was not successful. The athlete discarded the possibility of operative debridement of the tendon. Instead, an evaluation of the kinetic chain of the lower extremity and pelvic-lumbar area was performed, and the athlete was diagnosed with sacroiliac joint dysfunction and Achilles tendinitis. Evaluation findings, treatment program, and treatment outcome are also presented. The literature regarding sacroiliac joint mechanics and biomechanics of the foot-knee-hip and pelvic area is discussed and used to support the author's thesis that sacroiliac joint dysfunction, in this case a backward rotation of the right ilium, may have changed the kinematic chain of the lower extremity and caused a tendinitis in the Achilles tendon of the affected leg. Sacroiliac joint function and dysfunction, the reliability of sacroiliac joint mobility tests, and the validity of treatment programs are still considered controversial, and more research is needed to understand these mechanisms.