Aim. To analyze the prevalence and role of comorbidities in variety of clinical manifestations in patients with congenital occipital hypoplasia - «overcroded posterior cranial fossa» syndrome. Methods. Clinical history and physical examination of 200 patients (aged 16-74 years, males 108, females 92) with «overcrowded posterior cranial fossa» syndrome, including 134 with cerebellar ectopia, 92 with syringomyelia, 24 with hydrocephalus, were analyzed. Results. The diseases identified in patients with «overcrowded posterior cranial fossa» syndrome were combined into six groups: cardiovascular diseases (n=120; 60.0%), infectious and inflammatory diseases (n=39; 19.5%), gastrointestinal diseases (n=37; 18.5%), metabolic and endocrine diseases (n=31; 15.5%), diseases of the musculoskeletal system and connective tissue (including cervical vertebral stenosis (n=53; 26.5%), scoliosis (n=50; 25.0%), arthropathies (n=21; 10.5%), other diseases and pathological conditions (including mild traumatic brain injury (n=74; 37.0%), seizures (n=13; 6.5%). In patients with «overcrowded posterior cranial fossa» syndrome the prevalence of cardiovascular, gastrointestinal diseases, traumatic brain injury, obesity, primary or secondary cervical vertebral stenosis was significantly higher (p 0.05) compared to general population. In patients with syringomyelia a higher rate (p0.05) of scoliosis and traumatic brain injury was revealed. Conclusion. The prevalence of comorbidities in patients with «overcrowded posterior cranial fossa» syndrome was higher compared to general population. The differences of the type and rate of the concomitant diseases in patients with various forms of the syndrome may contribute to the variety of clinical manifestations of «overcrowded posterior cranial fossa» syndrome.