Recurrent aphthous stomatitis (RAS) is associated with endothelial dysfunction and chronic inflammation. The neutrophil-to-lymphocyte ratio (NLR) and mean platelet voume (MPV) are markers of inflammation and endothelial dysfunction, respectively. In the present report, we discuss the NLR and MPV values of patients with active and inactive RAS. In total, 42 patients (24 females and 18 males) with inactive RAS, 19 patients (12 females and 7 males) with active RAS and 40 healthy controls (24 females and 16 males) were enrolled. MPVs were measured and NLRs calculated. We sought correlations among the MPV and NLR findings in the active and inactive RAS groups and compared them with those of healthy controls. The MPV and NLR values were significantly higher in patients with active than inactive RAS (MPV, 10.6 ± 2.9 vs. 7.1 ± 2.4 fL, p < 0.001; NLR, 3.74 ± 1.9 vs. 2.1 ± 1.43, p = 0.015). In addition, both MPV and NLR values in patients with inactive RAS didn't differ significantly compared to values observed in the controls (MPV, 7.1 ± 2.4 vs. 6.9 ± 2.1 fL, p = 0.126; NLR, 2.1 ± 1.43 vs. 2.07 ± 0.96, p = 0.525). Both the NLR and MPV were significantly higher in patients with active RAS, emphasising the importance of inflammation and endothelial dysfunction in the pathophysiology of RAS activation.