A system for non-invasively determining an indication and/or an assessment of intracranial pressure (ICP) is featured. The system includes at least one intracranial light source adapted to be placed on skin above a cranium of a living subject configured to emit light which penetrates the cranium and targets intracranial space of a living subject. The system includes at least one extracranial light source adapted to be placed on skin above a predetermined area of the living subject configured to emit light which penetrates and targets extracranial space of the living subject. A detector subsystem including at least a first detector is configured to detect reflected light from the intracranial space and the extracranial space and is configured to output intracranial output signals associated with light detected from the intracranial space and/or output extracranial output signals associated with light detected from the extracranial space. A processing subsystem is coupled to the at least one intracranial light source, the at least one extracranial light source, and the detector subsystem. The processing subsystem is configured to determine intracranial oxygen saturation and extracranial oxygen saturation and non-invasively determine an indication and/or an assessment of ICP using a ratio of the intracranial oxygen saturation to the extracranial oxygen saturation.