We retrospectively examined the effect of combination therapy with prednisolone and cyclosporin-A (CSA) on the findings of pulmonary function tests (PFTs) and chest high-resolution computed tomography (HRCTs) scans in patients with dermatomyositis (DM) and acute/subacute interstitial pneumonia (A/SIP). We also examined whether CSA therapy improved PFT and chest HRCT findings. DM patients (n=14) with A/SIP were treated with 1 mg/kg/day prednisolone and 4 mg/kg/day CSA within 4.4 days (range, 1-12 days) from diagnosis. The trough level (C0) and 2-h post-dose blood concentration (C2) of CSA were measured. PFTs and HRCT scans were performed before and 1 year after treatment. The total ground-glass opacity area was calculated with the HRCT findings and used as the CT score. Combination prednisolone and CSA therapy improved the TLC%, VC%, FVC%, EFV1.0%, and CT score (P=0.027, 0.003, 0.002, 0.001, and 0.001, respectively). The C0 level was 178.8 ng/ml (range, 71-456 ng/ml), and the C2 level was 1,336.6 ng/ml (range, 814-2,873 ng/ml). Therapeutic changes in FVC%, FEV1.0%, and DLCO% were correlated with the C2 CSA level (P=0.047, 0.025, and 0.035, respectively). However, the PFT results and CT scan scores did not correlate with the daily dose or C0 level of CSA. Improvements in the CT score were correlated with time from IP diagnosis to CSA initiation (P=0.014). Early intervention with prednisolone and CSA combination therapy and tight control of the daily CSA dose by monitoring the C2 level improved PFT and chest HRCT findings in DM-A/SIP.