The Achilles tendon is a common site of acute and overuse injuries in runners. A case is described here in which the diagnosis of a post-traumatic intratendinous lesion was based on clinical examination and magnetic resonance imaging (MRI), and where conservative treatment was given. After a 6 months follow-up, symptoms as well as the MRI verified that intra-tendinous structural abnormalities had disappeared. This case report demonstrates that conservative treatment may be sufficient to cure Achilles injury with severe structural changes inside the tendon.