ABSTRACT Objectives We aimed to investigate the gender-based differences in idiopathic inflammatory myopathies (IIMs), with a particular focus on patient-reported outcomes, utilizing the data obtained through the international COVID-19 vaccination in autoimmune disease e-survey. Methods Patient-reported outcomes including fatigue, pain, and physical function were extracted from the COVID-19 vaccination in autoimmune disease database and compared between genders, adjusting for demographics and IIM subgroups by multivariable analysis. Inclusion body myositis (IBM) was analysed separately because of the substantial differences in outcomes. Results A total of 1197 complete responses from patients with IIMs as of 31 August 2021 were analysed. Seventy percent were women. Women were younger (58 [48–68] vs. 69 [58–75] years old, median [interquartile range], P < .001) and were more likely to suffer from autoimmune multimorbidity, defined as three or more autoimmune diseases in an individual patient (11.4% vs. 2.8%, P < .001). In non-IBM IIMs, fatigue visual analogue scale scores were higher in women (5 [3–7] vs. 4 [2–6], median [interquartile range], P = .004), whereas no significant gender-based differences were noted in IBM. Multivariable analysis in non-IBM IIMs revealed that women, residence in high-income countries, overlap myositis, and autoimmune multimorbidity were independently associated with increased fatigue. Conclusions Women with IIMs suffer from autoimmune multimorbidity and experience increased fatigue compared to men.