Background: Interstitial lung disease (ILD), is the main cause of mortality in Idiopathic inflammatory myopathy (IIM). Epidemiological, prognostic and treatment information are scarce. The goal was to characterize a cohort of IIM patients and compare response to immunosuppression (IS) among different types of IIM. Methods: Observational, multi-centric study in 30 centers from Argentina and Uruguay. Outcomes: Response to IS was defined as worsening: decline FVC >10%; improvement: increase FVC >10%; stability: changes FVC Results: We studied 56 patients with IIM; mean age 51 years; 77% women. 64% patients had anti-synthetase syndrome (ASS), and 36% had demarto/polymyositis. Mean FVC at baseline was 65 % and mean DLCO 55%. Tomographic patterns were nonspecific interstitial pneumonia (NSIP) in 46%, organizing pneumonia (OP) in 12%, overlap NSIP/OP in 17%. Only 55% had positive ANA. From ANA negative patients, 54% had at least one Anti-tRNA-synthetase antibody. Glucocorticoid (GC) were used in 95% of patients. 30% received GC pulses. Other IS drugs were cyclophosphamide, mycophenolate and azathioprine. For the overall cohort the outcomes were: stability 62%, improvement 32% and worsening 6% at 6-12 months. When analyzing response to IS, ASS had a better treatment response than other forms of IIM (OR 1.97 [95%CI 1.06-3.34]; p=0.03) for stability or improvement. Conclusions: ASS related ILD had a better treatment response than other forms of IIM in our cohort. ANA is often negative.