Previous reports have supported an association between tobacco smoking and cervical neoplasia. Our observations show an association between smoking and a reduction of the numerical densities of Langerhans cells and of helper/inducer T lymphocytes in the squamous epithelia of the transformation zone of the uterine cervix. This suggests a local impairment of cell-mediated immunity by smoking. This immunosuppressive effect could support the concept that smoking is an independent risk factor for cervical neoplasia.