Brachycephalicism and miniaturisation are risk factors for Chiari-like malformation (33). The condition is most commonly reported in toy breed dogs, in particular CKCS, King Charles spaniels, Griffon Bruxellois, Affenpinschers, Yorkshire terriers, Maltese, Chihuahuas, Pomeranians, Boston terriers and Papillons (34). Chiari-like malformation has also been recognised in cross-breed dogs particularly CKCS crosses. Partly because of its popularity as a pet, the Cavalier King Charles spaniel is overrepresented and Chiari malformation is considered ubiquitous in this breed (1, 31, 35). Up to 65% of the Griffon Bruxellois breed has Chiari-like malformation (21, 36); data for other breeds is not available. Chiari-like malformation may also be seen in cats and is again more common in brachycephalic varieties such as the Persian. The incidence of symptomatic Chiari-like malformation is not known and is difficult to determine because the most common clinical sign is pain. Pain is a complex amalgamation of sensation, emotions and (in humans) thoughts and manifests itself as pain behaviour which in a dog may not be recognised by owners or their veterinarians.In addition pain associated with Chiari-like malformation is rarely constant or focal. In humans the key features of Chiari-related headaches are their relationship to any Valsalva-like manoeuvre, their brief duration - often lasting only seconds – and their posterior, suboccipital location. In a dog this might manifest as a yelp on a rapid change of position, for example being picked up. It is difficult to attribute non-specific and brief signs to a specific aetiology especially when a condition is common in a breed and can be asymptomatic. The reported number of human patients with asymptomatic Chiari malformation type 1 varies between a third and a half of those diagnosed with the condition by MRI .