Which structure in the brain is the main source of cerebrospinal fluid production?

The choroid plexus is the main source of cerebrospinal fluid production in the brain.

It is a specialized vascular tissue found inside the cerebral ventricles. Its capillaries are covered by epithelial cells that filter and actively secrete components into the ventricular system, producing cerebrospinal fluid, or CSF. The blood vessels themselves are not directly exposed to the fluid because the epithelial layer forms an important barrier.

CSF cushions the brain and spinal cord, helps maintain a controlled chemical environment, and participates in waste transport. It circulates through the ventricles and subarachnoid space before being returned to the venous circulation through arachnoid granulations.

The choroid plexus is not the same as the blood–brain barrier throughout the brain, although its epithelial barrier is closely related in function. CSF production continues throughout life, and blockage or impaired absorption can contribute to hydrocephalus.