Monoplegia is paralysis of a single limb, usually an arm. Common symptoms associated with monoplegic patients are weakness, numbness, and pain in the affected limb. Monoplegia is a type of paralysis that falls under hemiplegia. While hemiplegia is paralysis of half of the body, monoplegia is localized to a single limb or to a specific region of the body. Monoplegia of the upper limb is sometimes referred to as brachial monoplegia, and that of the lower limb is called crural monoplegia. Monoplegia in the lower extremities is not as common of an occurrence as in the upper extremities. Monoparesis is a similar, but less severe, condition because one limb is very weak, not paralyzed. For more information, see paresis.

Many conditions that cause paraplegia or quadriplegia begin as monoplegia. Thus, the diagnosis of spinal paraplegia must also be consulted. In addition, multiple cerebral disorders that cause hemiplegia may begin as monoplegia. Monoplegia is also frequently associated with, and considered to be the mildest form of, cerebral palsy.