We report the case of a 49-year-old man who presented with pneumatosis cystoides intestinalis associated with polymyositis and interstitial pneumonia. Three months after the administration of prednisolone and cyclosporine, he noticed mild abdominal distension, and a radiographic examination showed intraperitoneal free gas and intramural gas, suggestive of pneumatosis cystoides intestinalis (PCI). Additional treatment with a combination of doxycycline and high-dose oxygen therapy was effective in relieving the clinical symptoms and reducing the intramural gas. © Japan College of Rheumatology and Springer-Verlag Tokyo 2004.