Myotilin is a Z-disc protein that binds alpha-actinin, gamma-filamin and F-actin. The essential role of myotilin in skeletal muscle is highlighted by the recent observation that autosomal dominant limb girdle muscular dystrophy type 1A is caused by mutations in the human myotilin gene. We studied the expression and subcellular distribution of myotilin in nemaline myopathy, central core disease, centronuclear myopathy, and myopathies with tubular aggregates. A prominent myotilin immunostaining of nemaline rods and core lesions was detected in all ten cases of nemaline myopathy and five cases of central core disease. This renders myotilin a sensitive, though non-specific marker for these structural lesions. Western blot analysis did not indicate an increased myotilin expression in nemaline myopathy muscle. However, the analysis indicated upregulation of a 75 kDa immunoreactive band, very weak in control muscle but previously detected in limb girdle muscular dystrophy 1A samples. Our findings indicate that myotilin is a core structural molecule in nemaline rods and central core lesions and suggest modification of myotilin in nemaline myopathy, and further support the notion that myotilin may have a key role in the dynamic molecular events mediating myofibril assembly in normal and diseased human skeletal muscle.