The goals of this study were to assess the predictive value of chart-abstracted American College of Rheumatology functional status (ACR-FS) with patient-reported ACR-FS and to relate it with measures of muscle function in a single-institution cohort of patients with idiopathic inflammatory myopathies (IIMs). Demographic and clinical data of 102 patients with IIMs regularly followed in the Rheumatology and Neurology Clinics at the University of Kentucky Medical Center between 2006 and 2012 were obtained through retrospective chart review. Clinical and functional status evaluation, muscle performance testing, and body composition measures were performed on a subset of 21 patients. ACR-FS was obtained by both chart abstraction and direct patient report. Spearman's correlations were used to examine the relationship of ACR-FS derived from chart abstraction with direct patient report, as well as the relationship of measures of physical function and body composition with ACR-FS. ACR-FS derived from chart abstraction was significantly correlated with ACR-FS derived from direct patient report (ρ = 0.78, p < 0.001). ACR-FS derived from chart abstraction was also significantly correlated with patient-reported physical function (ρ = -0.71, p < 0.001) and physical activity (ρ = -0.58, p < 0.05), manual muscle testing (ρ = -0.66, p < 0.01), and skeletal muscle endurance as measured by the functional index-2 test (shoulder flexion ρ = -0.62, p < 0.01; hip flexion ρ = -0.65, p < 0.0; heel lift ρ = -0.67, p < 0.01; and toe lift ρ = -0.68, p < 0.01). The ACR-FS is a simple measure of disability that can be used in chart abstraction studies involving IIM patients. We have demonstrated that ACR-FS correlates well with muscle performance tests of strength and endurance.