Most of the disturbances of autonomic system (AS) activity seen in clinical practice result from head injury are due to development of increased intracranial pressure (ICP). It has been described that cerebral lesions produce hypersympathetic states mediated mostly by sympatho-adrenal discharge. Aim of the study was to evaluate effects of ICP on heart rate variability (HRV) in patients with brain tumors. We studied 24 patients, which were divided on two groups: with increased ICP before neurosurgery treatment caused by brain tumors with symptoms and without symptoms with treated ICP. Our results provided evidence that all patients with increased ICP had the autonomic system disturbances. The heart rate variability and cardiovascular reflexes are useful in identification of autonomic system dysfunction.