We examined peripheral gamma delta T cells in patients with severe neurologic impairment. The gamma delta T cells in these patients significantly increased as compared with those in healthy adults (P < 0.0001). These cells expressed the V gamma 9/V delta 2 phenotype which was reported to proliferate by infections. When patients with severe neurologic impairment and patients with Duchenne muscular dystrophy (DMD) were divided into frequent and non-frequent infectious groups, the gamma delta T cells increased significantly in the frequent infectious group of DMD (P < 0.005), but not significantly in the frequent infectious group of patients with severe neurologic impairment. These results indicated that the gamma delta T cells of patients with severe neurologic impairment increased in frequent infections and other factor(s).