60 patients with a complete Achilles tendon rupture were randomized to either surgical repair or nonoperative treatment with immobilization followed by rehabilitation. Patients were assessed on magnetic resonance imaging (MRI) for calf muscle volume, fatty degradation of the soleus and medial and lateral gastrocnemius, and Achilles tendon length. The only significant difference between groups in muscle volume was observed in the soleus, which demonstrated a significantly smaller difference between the affected and unaffected limbs at 18 months in the surgical repair group compared to the nonoperative group.