<h3>Background</h3> Prevalence of comorbidities and their impact on health outcomes in Idiopathic inflammatory myopathies (IIMs) is limited. <h3>Objectives</h3> This study aimed to explore the prevalence of multimorbidity in patients with IIMs, other autoimmune rheumatic diseases (AIRDs) and Healthy controls (HCs). We further explore the impact of comorbidities on patients' physical, mental, and social health assessed by the Patient-Reported Outcome Measurement Information System (PROMIS instruments). <h3>Methods</h3> Data for this study were acquired from the COVAD 2 e-survey hosted by a study group consisting of 167 collaborators in 110 countries. Basic multimorbidity (BM) was defined as the co-occurrence of two or more comorbidities in an individual, while complex multimorbidity (CM) signified the co-occurrence of 3 or more chronic conditions affecting 3 or more different organ systems. PROMIS global physical health (PGP), mental health (PGM), fatigue 4a (F4a) and physical function short form (SF10) were analysed using descriptive statistics and linear regression models. Hierarchical Clustering on Principal Components was performed to outline the grouping. <h3>Results</h3> Of 10740 complete respondents, 1558 IIMs, 4591 AIRDs and 3652 HCs were analysed. Individuals with IIMs exhibited high burden of any comorbidity (OR: 1.62 vs AIRDs and 2.95 vs HCs,p&lt;0.01), BM (OR 1.66 vs AIRDs and 3.52 vs HCs,p&lt;0.01), CM (OR: 1.69 vs AIRDs and 6.23 vs HCs,p&lt;0.01), and mental health disorders (MHDs) (OR 1.33 vs AIRDs and 2.63 vs HCs,p&lt;0.01). IIM patients with comorbidities (and MHDs) had worse physical function (low PGP, PGM, SF10 and higher F4a scores, all p&lt;0.001). Worse physical function (PGP) was predicted by age (0.35; 0.030), active disease (-1.51; &lt;0.001), BM (-1.11; &lt;0.001), and MHDs (-1.47; &lt;0.001). PGM was impacted by age (0.51; 0.004), active disease (-1.34, &lt;0.001), BM (-0.75; 0.001) and MHDs (-2.22; &lt;0.001). Determinants of SF10a were age (-3.86; &lt;0.001), active disease (-7.03, &lt;0.001), female (2.85, &lt;0.001), BM (-2.95; &lt;0.001) and MHDs (-2.37; &lt;0.001). Fatigue (F4a) was impacted by age (-0.96, &lt;0.001), active disease (1.45, &lt;0.001), country human development index (0.95; 0.036), BM (1.11; &lt;0.001); and MHDs (2.17; &lt;0.001). Four distinct clusters (Figure 1A, Table 1) were identified i.e., cluster 0: lower burden of comorbidities and good health status; cluster 1: older patients, whit higher burden of comorbidities and poor health status, cluster 2: patients with higher prevalence of MHDs, lower PGP and PGM; and higher F4a scores; and lastly Cluster 3 that comprised older patients with an average burden of comorbidities and overall good health status according to PROMIS scores. Dermatomyositis, anti-synthetase syndrome, necrotizing autoimmune myopathy were similarly represented in all clusters, whilst inclusion body myositis and polymyositis were more predominant in clusters 1 (40.6% and 17.2%) and 3 (32 % and 17.5%), while overlap myositis was more represented in cluster 2 (25.6%) and 0 (32.7%) (Figure 1B). <h3>Conclusion</h3> Patients with IIMs have a higher burden of comorbidities that adversely impact physical and mental health, calling for optimized approaches for holistic patient management. <h3>REFERENCES:</h3> NIL. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Marco Fornaro: None declared, Vincenzo Venerito: None declared, Florenzo Iannone: None declared, Naveen Ravichandran: None declared, Elena Nikiphorou: None declared, Mrudula Joshi: None declared, Ai Lyn Tan: None declared, Sreoshy Saha: None declared, Samuel Katsuyuki Shinjo: None declared, Vishwesh Agarwal: None declared, Nelly Ziade: None declared, Tsvetelina Velikova: None declared, Kshitij Jagtap: None declared, Marcin Milchert: None declared, Ioannis Parodis: None declared, Abraham Edgar Gracia-Ramos: None declared, Lorenzo Cavagna: None declared, Masataka Kuwana: None declared, Johannes Knitza: None declared, Ashima Makol: None declared, Dey Dzifa: None declared, Carlos Enrique Toro Gutierrez: None declared, Carlo Vinicio Caballero: None declared, Oliver Distler Shareholder of: OD has/had consultancy relationship with and/or has received research funding from and/or has served as a speaker for the following companies in the area of potential treatments for systemic sclerosis and its complications in the last three calendar years: 4P-Pharma, Abbvie, Acceleron, Alcimed, Altavant, Amgen, AnaMar, Arxx, AstraZeneca, Baecon, Blade, Bayer, Boehringer Ingelheim, Corbus, CSL Behring, Galderma, Galapagos, Glenmark, Gossamer, iQvia, Horizon, Inventiva, Janssen, Kymera, Lupin, Medscape, Merck, Miltenyi Biotec, Mitsubishi Tanabe, Novartis, Prometheus, Redxpharma, Roivant, Sanofi and Topadur. Patent issued "mir-29 for the treatment of systemic sclerosis" (US8247389, EP2331143)., Jessica Day: None declared, COVAD Study: None declared, Hector Chinoy: None declared, Vikas Agarwal: None declared, Rohit Aggarwal Shareholder of: RA has a consultancy relationship with and/or has received research funding from the following companies: Bristol Myers-Squibb, Pfizer, Genentech, Octapharma, CSL Behring, Mallinckrodt, AstraZeneca, Corbus, Kezar, Abbvie, Janssen, Kyverna Alexion, Argenx, Q32, EMD-Serono, Boehringer Ingelheim, Roivant, Merck, Galapagos, Actigraph, Scipher, Horizon Therapeutics, Teva, Beigene, ANI Pharmaceuticals, Biogen, Nuvig, Capella Bioscience, and CabalettaBio., Latika Gupta: None declared.