Quantitative magnetic resonance imaging (qMRI) has recently shown its benefit in a longitudinal study of lower limb muscles in dysferlinopathy. This study has demonstrated the differential muscle involvement by measuring muscle fat fraction (FF) and significant yearly increases in FF. Additionally, muscle water T2, reflecting the disease activity (i.e. inflammation, edema), was found to be persistently elevated. Other anatomical regions are known to be affected later in the disease progression of dysferlinopathy, so upper limb muscles were investigated in a follow-up natural history study, Jain COS2. Here, we report preliminary baseline results. The qMRI data were acquired on two 3-tesla clinical systems at two centers in Europe between July 2019 and March 2022, in patients (n=27) and controls (n=4). qMRI acquisitions included fat-water imaging and water T2 mapping at the level of the arm (deltoid, triceps, biceps brachialis) and forearm (extensor, flexor). Student's t-tests were performed (P<0.05). Overall, patients (13 female, 14 male, 61% ambulant) were 41±12 years old and had symptoms for 17±9 years. No differences in demographic data for age, sex and years since symptoms existed between sites (P>0.132) although patients were slightly younger in site 1. Whereas in site 2, albeit one patient was assigned to limb-girdle muscular dystrophy type R2 (LGMD R2), site 2 patients were assigned to LGMD R2 or Miyoshi myopathy/other phenotypes in a 50/50 ratio (P=0.004). For all investigated muscles, FF values were significantly higher in patients than in controls (P<0.001). Although FF values were lower in patients at site 1, differences with site 2 were not significant (P<0.125). The lowest FF values were observed in the extensor muscle (site 1: 12.0±6.0%, site 2: 12.1±6.0%, P=0.463) while the highest FF was seen in deltoid muscle (site 1: 27.4±19.0%, site 2: 32.1±21.4%, P=0.278), confirming the predominant proximo-distal muscle involvement in dysferlinopathy. Muscle involvement showed a high inter-individual patient variability, at least for the arm muscles. Water T2 values were increased as compared to controls (90% percentile in controls = 36.5ms) in triceps muscle in both sites (site 1: 39.3±3.0 ms, site 2: 37.2±4.9 ms), which is in line with the finding of elevated water T2 values in lower limb in earlier work. These baseline qMRI results give a quantitative view on the disease progression and activity in the upper limb muscles of dysferlinopathy patients.