Introduction: Working in coal mines is a risk factor for pneumoconiosis and COPD. There still exist, however, doubts and debates about the risk involved in such work for tuberculosis and lung cancer. The aim of this study was to clarify some of these uncertainties through the study of a cohort group. Methods: The cohort comprises 2,579 miners. An initial medical examination was carried out when they began to work in the mine, and three further examinations were performed over the 20 years of the study. The follow-up failure rate was 23.7%. Results: Ninety-nine workers (3.8%) developed round opacities (category 1) that were significantly related to the kind of work in a crude analysis (p 0.045), with a greater frequency (7.3%) among rock workers, who have greater exposure to silica, and were almost significantly related to tobacco use (p 0.092). These round opacities also show a significant relation to smoking, being more frequent (4.9%) among smokers, both in the crude analysis (p 0.028) and in the multivariable analysis (p 0.001) controlling for rock work. In 240 workers (12.7%), accelerated FEV1 decreases were observed with significant relations to tobacco use (p 0.001) and rock work (p 0.044). Pulmonary tuberculosis was diagnosed in four cases, with an incidence of eight in 10 5 person-years. This rate falls within the limits expected for the region. No case of lung cancer was observed. Conclusion: In summary, our results showed the following: round opacities (category 1) were related to smoking and, probably, to rock work; accelerated FEV1 decreases were related to rock work and tobacco consumption. There was no identified increase in tuberculosis or lung cancer in this cohort. (CHEST 2004; 126:622– 629)