Vitiligo progression is attributed to immune system malfunctioning, thus immunomodulating compounds might be beneficial in stopping vitiligo progression which is a prerequisite for successful repigmentation. The goal of this study was to assess efficacy of acridone acetic acid, sodium salt (Na-AAA), an immunomodulating compound with favorable safety profile, in stabilizing active vitiligo, and to reveal prognostic factors of treatment outcome. Sixty consecutive patients with progressing nonsegmental vitiligo were treated with 10 i.m. injections of Na-AAA every other day. Disease stability was assessed in 1, 3, 6, and 12 months post-treatment. Statistical analysis was applied to correlate treatment outcome and available clinical parameters. Of the 60 patients treated, vitiligo stopped progression in 44 patients (73.3%). Older age (p = 0.0219), age of 35 and older (p = 0.0189, odds ratio (OR) = 5.2, 95% confidence interval (CI) 1.30–20.84) or age of 40 and older (p = 0.0039, OR = 6.48, 95% CI 1.86–22.61), longer disease duration (p = 0.0234), pre-treatment interleukin-6 level over 2 pg/mL (p = 0.0005, OR = 13.7, 95% CI 2.97–63), and over the reference threshold value 5.9 pg/mL (p = 0.0009, OR = 25.8, 95% CI 2.8–239) as well as presence of other autoimmune diseases (p = 0.038, OR = 7.0, 95% CI 1.14–42.97) were negative prognostic factors of treatment success. In conclusion, acridone acetic acid, sodium salt, emerges as an efficient option for stopping vitiligo progression.