Achilles tendinitis is an injury that commonly affects athletes in the running and jumping sports. It results from repetitive eccentric load-induced microtrauma that stresses the peritendinous structures causing inflammation. Achilles tendinitis may be classified histologically as peritendinitis, tendinosis, or partial tendon rupture. Training errors are frequently responsible for the onset of Achilles tendinitis. These include excessive running mileage and training intensity, hill running, running on hard or uneven surfaces, and wearing poorly designed running shoes. Biomechanical abnormalities that predispose to Achilles tendinitis include gastrocnemius-soleus muscle weakness or inflexibility and hindfoot malalignment with foot hyperpronation. The initial treatment should be conservative with relative rest, gastrocnemius-soleus rehabilitation, cryotherapy, heel lifts, nonsteroidal anti-inflammatory drugs, and correction of biomechanical abnormalities. Surgery is recommended only for persons with chronic symptoms who wish to continue running and have not benefited from conservative therapy.