Nemaline myopathy (also called rod myopathy or nemaline rod myopathy) is a congenital, often hereditary neuromuscular disorder with many symptoms that can occur such as muscle weakness, hypoventilation, swallowing dysfunction, and impaired speech ability. The severity of these symptoms varies and can change throughout one's life to some extent. The prevalence is estimated at 1 in 50,000 live births. It is the most common non-dystrophic myopathy.

"Myopathy" means muscle disease. Muscle fibers from a person with nemaline myopathy contains thread-like rods, sometimes called nemaline bodies. While the rods are diagnostic of the disorder, they are more likely a byproduct of the disease process rather than causing any dysfunction on their own. People with nemaline myopathy (NM) usually experience delayed motor development, or no motor development in severe cases, and weakness may occur in all of the skeletal muscles, such as muscles in the arms, legs, torso, neck flexors, throat, and face. The weakness tends to be more severe in the proximal muscles rather than the distal muscles. The ocular muscles are normally spared.

The disorder is often clinically categorized into groups with wide ranges of overlapping severity, from the most severe neonatal form which is incompatible with life, to a form so mild that it may not be diagnosed since the person appears to function at the lowest end of normal strength and breathing adequacy. Sporadic late onset nemaline myopathy (SLONM) is not a congenital disorder and is considered a different muscle disease from NM, which has its onset at birth or early childhood. Respiratory problems are usually a primary concern for people with all forms of NM, and respiratory infections are quite common. NM shortens life expectancy, particularly in the more severe forms, but aggressive and proactive care allows most individuals to survive and even lead active lives.

Nemaline myopathy is one of the neuromuscular diseases covered by the Muscular Dystrophy Association in the United States.