A 45 years old female runner developed a bilateral tendinopathy of the Achilles tendon after repeated antimicrobiotical treatment with ciprofloxacin. One month later the right Achilles tendon ruptured without any sudden pain. MRI revealed degenerative changes of the left Achilles tendon; on the right side the tendon was ruptured with a dehiscence of 4 cm between both ends of the tendon. The tendon was reconstructed surgically. The histological analysis showed cystic changes with focal necrosis. This finding differ from findings in non drug induced tendinopathies. After antimicrobiotical treatment with ciprofloxacin the side effect of a tendon disorder must be considered. The impairment of the tendon may be as strong that a tendon rupture may occur at daily living activities without any typical clinical symptoms.