The International Labour Office (ILO) classification of radiographs of pneumoconiosis is a standard means of assessing the presence or absence of pneumoconiosis in workers exposed to mineral dusts. Using this classification, 200 admission chest radiographs were reviewed on hospitalized patients in an urban university medical center to determine the prevalence and possible significance of "small opacities" in a population without known industrial exposure. Seventy-one men and 129 women were screened with the mean age of 44.2 years (range, 15-84). Thirty-six (18%) of the 200 patients had small opacities at profusion level 1/0 or greater, and this constituted the "positive radiographs" group. Twenty-two patients (11%) with positive radiographs had no documentable dust exposure or other specific medical etiology that would explain the presence of their lung opacities. The high prevalence of small opacities in "normal" older individuals has important implications in the assessment of patients with suspected pneumoconiosis.