Section 1 is a general introduction to the cavalier King Charles spaniel and the neurological diseases of the breed. Section 2.1 encompasses the first description of the disease and its proposed pathogenesis. As knowledge and understanding has improved this description is refined in section 2.2 and a novel hypothesis for the pathogenesis is presented. Section 3 compares and contrasts canine Chiari-like malformation (occipital hypoplasia) with the other common developmental defect of the occipital bone – occipital dysplasia. Section 4 details a study investigating intracranial and cervical dimensions and their relationship to the development of syringomyelia. Section 5.1 and 5.2 discuss how CM/SM results in the clinical signs that it does, with particular regard to pain. Section 5.2 also postulates the most appropriate medical treatment. Section 6 discusses the surgical management of the condition and describes a brief pilot study investigating conservative management. Section 7 discusses the possible hereditary nature of the condition and details the work in progress to investigate the causative genes. In section 8 the thesis is summarized and future plans for continuing this research are detailed.