Anti-RNA polymerase III antibodies (ARA) are a specific marker for Systemic Sclerosis (SSc), associated to severe disease with major organ and diffuse cutaneous involvement. In our series, ARA were found in 19 of 216 sera, in 15 cases as isolated antibodies' specificity, with a statistically negative association with other SSc-specific autoantibodies (p: 0.00003). The prevalence of ARA among 73 anticentromere and anti-topoisomerase I (topo I) negative sera, was 20.5%. Patients with isolated ARA had more rapid disease onset, defined as the interval from the appearance of Raynaud's phenomenon to the first symptom other than Raynaud's, than patients with isolated anti-topo I antibodies (median: 2 months vs 13 months; p: 0.0013). A rapid onset of SSc (within 6 months from Raynaud's phenomenon onset) was found in all patients with isolated ARA and only in 34% of those with anti-topo I (p<0.00001). Moreover, the skin thickening in the first months after SSc onset was faster in the ARA group (p<0.0001). Nevertheless, the rates of internal organ involvement and of survival rates were similar between the two groups. Our experience therefore suggests that ARA are a marker of very rapid onset of disease and skin thickening progression in SSc.