Three hundred and sixty four patients with Chiari malformation (CM) type I were examined: 263--with isolated CM and 101--with concomitant syringomyelia (SM). To study clinical features of the disease, neurological examination, craniography and magnetic resonance imaging of the brain and spinal cord were used. Similar predisposing factors and groups of objective neurological symptoms were found. Differences in the first subjective appearance and age at the disease onset were revealed. In patients with isolated CM, brain stem and cerebella symptoms dominated in the clinical picture, with spinal disturbances and asymptomatic cases being sometimes found. In patients with CM + SM, brain stem and spinal disturbances were more frequent and severe, comparing to those with single CM. Similar clinical features are due probably to common disease pathogenesis and the different ones are the result of the cerebrospinal fluid disturbances, causing intracranial hypertension, hydrocephaly and SM.