Exposure to tobacco smoke is widespread; nearly everyone is exposed at one time or, another. Many of us are exposed on a regular basis in homes, offices, vehicles, and public places. Many of the over 2,000 identified compounds in tobacco smoke are established carcinogens, asphyxiants, and eye, nose, or respiratory irritants. While health effects of smoking on smokers have been clearly and carefully documented, only recently have investigations into the possible health effects of sidestream tobacco smoke on nonsmokers been undertaken. This paper reviews recent research, including studies on the influence of parental smoking on the respiratory health of children and the incidence of lung cancer in women with smoking husbands. While results from some of the studies are unclear, consistent relationships between respiratory health and tobacco smoke exposure have been documented. The need for a careful evaluation of the public health significance of exposure to sidestream tobacco smoke is emphasized.