© 2021 Elsevier Inc.Objective: The aim of this study was to determine the frequency of sarcopenia at the time of diagnosis in patients with rheumatoid arthritis (RA), assessing disease activity and factors that may be associated with sarcopenia and observe effects of treatment on sarcopenia. Method: A prospective study was conducted with patients who have newly diagnosed RA. Patients were evaluated twice, at the time of diagnosis and 3 mo after the initiation of treatment. Demographic data, anthropometric measurements, disease activity scores, and sarcopenia status were recorded. Sarcopenia was evaluated with grip strength and bioelectric impedance. The results were compared with healthy volunteers. Results: The age at onset of RA was 50.6 ± 14.6 y. Handgrip strength (P < 0.001), skeletal muscle mass (P = 0.009), and skeletal muscle mass index (P = 0.032) were reduced in patients with RA but not in the control group. The frequency of sarcopenia in RA at onset of diagnosis was 31.5%. There was a significant decrease in the rate of sarcopenia after 3 mo of treatment (31.5 versus 8.7%; P = 0.046). Conclusion: Sarcopenia was found in approximately one-third of the patients with newly diagnosed RA in our study. With treatment, sarcopenia improved significantly. Patients with RA should be evaluated in terms of sarcopenia in addition to evaluating joint and extraarticular findings at the time of diagnosis. Early detection and treatment planning may improve quality of life.