Seventeen cases of ataxia telangiectasia (AT) were diagnosed over a period of 10 years. The children affected by AT were aged about 7 years and they were preferentially males (67%). The principal clinical aspects were: cerebellous ataxia (98%), recurrent ENT infections (86%) and ocular telangiectasia (96%). We also showed an immune function defect mainly concerning IgA, which was associated with cellular immunity abnormalities (lymphopenia, negative hypersensitivity reactions). The alpha-fetoprotein (AFP) values were high and increased in proportion to the severity of the neurologic manifestations. Thus, this parameter could be used as a diagnostic index of the illness and could be a precious indicator for the management and the evolution of these patients.