To assist in making prognoses for patients with interstitial pneumonia (IP) who were treated with cyclosporin A (CsA), we conducted a review of forty-nine patients (32 men and 17 women with a mean age of 62 yrs) with progressive IP during the period from 1997 through 2001. All patients were steroid-resistant or acutely exacerbated cases. They received a low dosage of CsA (100-130 mg/day) combined with corticosteroids. Before and after the CsA therapy, blood gas analysis and HRCT scans were evaluated. Twenty-five patients underwent video-assisted thoracoscopic surgery (VATS) or autopsy for a histopathological evaluation. Among the 49 patients with IP, the documented underlying systemic diseases were of unknown etiology (IPF or IIP) in 26 and were collagen vascular diseases (CVD) in 23. The chest CT pattern and underlying systemic diseases of IP were classified as a usual interstitial pneumonia (UIP) pattern/IPF in 16 cases, a non-UIP pattern/IIP in 10 cases, a UIP pattern/CVD in 7 cases, and a non-UIP pattern/CVD in 16 cases. The prognoses after CsA treatment were improved or unchanged in 27% of cases with a UIP pattern/IPF, 78% of cases with a non-UIP pattern/IIP, 71% of cases with a UIP pattern/CVD and 75% of cases with a non-UIP pattern/CVD; deteriorated in 73%, 22%, 29% and 25% of cases, respectively, with these patterns and underlying diseases. At present, four out of thirteen (31%) patients with acute exacerbation of UIP pattern/IPF have survived for four to twelve months (mean: 7.5 months). Four patients revealed re-exacerbation of IP after the dose of CsA was tapered. Among the 25 patients with IP, the histopathological patterns of IP were classified as usual interstitial pneumonia (UIP) in 10 cases, nonspecific interstitial pneumonia (NSIP) in 14 cases (group I, 2; group II, 5; group III, 7) and diffuse alveolar damage (DAD) in 1 case. The prognoses were improved or unchanged in all cases of NSIP group I, in 80% of cases with NSIP group II, in 29% of cases of NSIP group III and in 20% of cases of UIP; and deteriorated in the case of DAD, in 80% of cases of UIP, in 71% of cases of NSIP group III, and in 20% of cases of NSIP group II. It should be emphasized that CsA combined with corticosteroids may be effective for the treatment of steroid-resistant or acute exacerbation cases of IP. Further studies are required to determine long-term outcome with this treatment.