A case-control study was carried out to assess the association between pneumatosis cystoides intestinalis (PCI) and working conditions, including occupational exposure to organic solvents. Thirteen patients with primary PCI were individually matched with controls by sex, age, and admission year. It was found that there was a close association between the development of primary PCI and occupational exposure to trichloroethylene (TCE). Twelve of 13 patients with PCI (92.3%) were found to have been exposed occupationally to TCE, and the healing and recurrence of PCI in these patients substantially paralleled the profile of their occupational exposure to TCE. Two pairs of patients with PCI had been working in the same factories, where they had degreased camera lenses with TCE. These results suggest that chronic exposure to TCE could be one of the etiological factors in PCI.