Since 1990, a cohort survey has been carried out among workers employed in pottery workers by the Local Health Unit of Viterbo, Latium (Italy). Cumulative exposure to silica containing dust has been assessed for 808 workers, who were also screened with a questionnaire on respiratory symptoms, chest radiography and lungfunction tests. The prevalence of small opacities 1/0 and 1/1+ was 3.0% and 4.1% respectively and the prevalence increased with the cumulative exposure. A close relationship has been found between silica dose and decrease in lung function.