This study aims to describe the patient perspective on glucocorticoid (GC) treatment and adverse effects (AEs) in idiopathic inflammatory myopathy (IIM). An online survey was distributed to patients with adult-onset IIM using the Myositis UK page on Healthunlocked.com, an online social network for health. Respondents were asked to rate the severity of AEs they attributed to GCs on a Likert scale (0-5), and to report concerns and overall experience of GC treatment. The survey was completed by 122 respondents. The median reported current daily dose of prednisolone was 15 mg (interquartile range [IQR] 8, 25) and median treatment duration 5.3 years (IQR 3.4, 8.0) at the time of survey completion. Only 54% of respondents “agreed” or “strongly agreed” that the information provided to them about GC treatment was adequate. AEs rated most severe by respondents were weight gain, moon face, sleep disturbances and increased hunger. The duration of GC treatment weakly correlated with the mean number of reported AEs (p = 0.004) and mean severity of AEs (p = 0.017). There was an inverse relationship between age and acne, stretch marks, hair loss, facial hair, nausea and heartburn (p < 0.05). In this first study of patient-reported experiences of GCs specifically in IIM, we describe the burden of treatment and highlight the unmet need for safe and well-tolerated treatments. We report that patients with IIM often remain on long-term GC treatment at moderate doses, and that AEs are common. The reported data will be useful in planning discussions with patients regarding adherence to their treatment options. Key Points • Glucocorticoids (GC) are the first-line treatment in patients with idiopathic inflammatory myopathies (IIM), and are associated with a wide range of adverse effects • The adverse effects related to GC are very common, and those reported most severe by patients included weight gain, moon face, increased hunger or sleep disturbance, which may differ from the primary concerns of their treating clinician • Understanding the patient perspective and concerns about treatment is necessary to maintain a good physician-patient relationship and may help with treatment adherence.