Abstract Objective To describe trends in outcomes among patients with idiopathic inflammatory myopathies (IIM) over two decades. Methods From 1997 to 2017, a total of 1079 IIM patients were documented in the National Database of the German Collaborative Arthritis Centers. Annual cross-sectional data on treatment, disease activity, patient-reported outcomes, hospitalization and employment were compared across the years. Information on phenotypes, organ manifestations and autoantibodies was collected for a subset to compare the assessment of global health, pain, fatigue and sleeping disorders. Results In 2017, significantly more IIM patients were assessed to be in low disease activity (94%) than in 1997 (59%), p < 0.01. Pain (p = 0.001), global health (p = 0.049), fatigue (p = 0.03) and sleeping disorders (p = 0.01) also improved since recording. Glucocorticoid use decreased from 84 to 58% (p < 0.01). Employment in patients < 65 years remained unchanged (53%), while early retirement (23–9%), hospitalization/year (34–18%) and sick leave (52–24%) decreased. A total of 186 patients with information on subtypes were classified as polymyositis (44%), dermatomyositis (33%), anti-synthetase syndrome (10%), overlapping-myositis (8%), inclusion body myositis (2%), necrotizing myositis (0.5%) and unspecific (3%). The most frequently reported symptoms were limitations in global health (60%), fatigue (57%) and sleeping disorders (51%), and all of them were most frequent in overlap-myositis. Pulmonary hypertension and cardiomyopathy were associated with poor outcomes regarding global health, daily activities and fatigue. Conclusion IIM patients report better outcomes than 20 years ago, along with good physician-reported disease control. Global health, fatigue and sleeping disorders are relevant patient-reported domains in IIM.