The current study was undertaken to assess the relationship of smoking to the risk of lens opacities. The risk was evaluated separately for nuclear and cortical opacities and for both types together. We studied 838 watermen in Maryland by detailed ocular examination for the presence and severity of each cataract type. All subjects were interviewed regarding smoking history, and a cumulative smoking dose was calculated. The results suggest a significantly increased risk of pure nuclear opacities associated with cigarette smoking. The increase in smoking dose was associated with increasing severity of nuclear opacity. The risk of nuclear opacities increased with increasing cigarette dose and decreased if the subject had quit smoking. The effect of smoking was most striking in those less than 80 years old. No increased risk of nuclear opacities was observed with earlier age when smoking started, after adjusting for dose and cessation of smoking. Further investigations are warranted on the biochemical and physical damage to the nucleus of the lens from smoking cigarettes.