To assess whether the evolution to pneumoconiosis may be suspected in coal miners, we conducted a 4-yr longitudinal study of 80 dust-exposed miners with chest X-ray findings classified 0/1 or 1/0 according to the International Labor Organization (ILO) classification (exposed to coal mine dust, suspected of pneumoconiosis [ES group]) and two control groups having normal X-rays. The first of these latter two groups included 80 miners with similar exposure to that of the first group (exposure with normal X-rays [EN]), whereas the second group consisted of markedly less exposed miners (no exposure with normal X-rays [NN]). The protocol comprised a questionnaire on respiratory symptoms and smoking, assessment of cumulative coal-mine-dust exposure, X-rays, computed tomographic (CT) scans, and lung-function tests. The study was conducted in 1990 and 1994 by the same medical team. At the end of the follow-up, 24 members of the ES group had worsened X-ray findings, and 10 of them had X-ray findings classified as 1/1 or greater. In the EN and NN groups, six and one subjects, respectively, had worsened X-ray findings. At the first examination, subjects who developed pneumoconiosis had significantly lower values for FEV1/FVC ratio, maximum midexpiratory flow (MMEF), and maximal forced expiratory flow at 25% of vital capacity (FEF25%), and higher CT-scan micronodule scores. This latter score and FEF25% were significantly associated with the evolution to pneumoconiosis in the ES group, and scanner micronodule score and MMEF were significantly associated with this in all three groups combined. Worsening findings on X-ray and change to pneumoconiosis must be controlled in coal miners. The findings in this study offer the possibility of identifying miners who especially need follow-up and monitoring.