We report two cases of spastic cerebral palsy classified as diplegia-type complicated cervical spondylotic myelopathy. Under the Gross Motor Function Classification System (GMFCS), both were classified as Level IV, defined as standing with support, but with difficultly, after the diagnosis of cervical spondylotic myelopathy. Paralysis in both the upper and lower limbs deteriorated and became a form of quadriplegia. In one case, there was no appeal from the patient even after the manifestation of symptoms；diagnosis and surgery were both time consuming, with no improvements in post-operative symptoms including urinary incontinence. In the other case, early diagnosis was possible and operation was scheduled early. The post-operative response was positive, and the patient was able to recover to pre-cervical spondylotic myelopathy conditions. Complications of cervical spondylotic myelopathy is well-known in the athetosis type；however, reports on the spastic type are limited. Here, we report complications of cervical spondylotic myelopathy in spastic cerebral palsy and show that early detection and surgery are important factors in mitigating long-term recovery.