We present a 50-year-old woman who sustained spastic left hemiplegia secondary to the right thalamic hemorrhage 6 years ago. She complained of persistent severe left calf pain after serial casting for the treatment of shortened plantar flexors of the left ankle. Two months later, magnetic resonance T1-weighted images showed diffuse high signal intensity involving the whole muscle bulk of the soleus and normal signal intensity of thin atrophied gastrocnemius. Needle electromyography of the soleus revealed myopathic patterns. Histologic findings of the soleus showed necrotic muscle fibers with phagocytosis, endomyseal collagen and fat deposition. We concluded that prolonged passive stretch of spastic plantar flexors of the ankle under serial casting induced soleus myopathy with segmental myonecrosis, and which developed left calf pain. Selective induction of soleus myopathy could be explained by the higher stretch tension produced by ankle dorsiflexion in the soleus compared to the gastrocnemius because of different proximal ends.