Idiopathic inflammatory myopathy (IIM), commonly referred to as "myositis", is a rare but treatable auto-immune disease that is often misdiagnosed or diagnosed after significant delay. Using three clinical case reports as introductory examples, an overview is given - and pitfalls are discussed - of the diagnosis and treatment of myositis. Disease features are often extra-muscular in nature, may vary considerably between patients, and are frequently non-specific. Myositis-related morbidity is high and myositis can be fatal, mainly due to cancer and interstitial lung disease. As such, we stress the importance of early recognition of this severe disease and timely referral of a patient with a (suspected) IIM to a multidisciplinary team for optimal diagnosis and disease management.