Introduction To this day, there is limited information on the language pathology of patients with PSP, an atypical Parkinson’s syndrome which leads to language impairments such as reduced word fluency, syntactic difficulties, reduced speech output, and impaired sentence completion. While there is evidence of success of tDCS for word fluency [1, 2, 3], little is known about the effectiveness of brain stimulation for sentence completion. In this study, we investigated whether tDCS improves language in PSP patients by reducing the time they need to complete sentences. Materials and Methods 5 patients with PSP (4m; age: ∅=72.6y ± 5.8; duration of illness: ∅=3.6y, SD=1.7) participated in this double-blinded and sham-controlled study. To stimulate the left Broca’s area, we used tDCS with 2 mA for 20 min. The cathode was placed supraorbitally on the right hemisphere. The patients completed 50 auditorily presented sentences in both a tDCS and a sham stimulation session. Each setting had a comparable set of sentences concerning sentence type, concreteness, and length. The statistical analysis was performed with paired samples t -tests using jamovi [4]. Results Out of 5 patients, 4 individuals were faster at word retrieval for sentence completion when tDCS was applied, with an average response time of 2331 ms with tDCS and 3187 ms with sham stimulation. The difference between tDCS and sham is slightly above significance for all patients together ( t =1.71, p =.08). Strikingly, disease duration may be related to the difference between tDCS and sham treatment. Patients 1 and 2, who had their first symptoms only 2 years ago, showed the smallest response time difference between tDCS and sham treatment ( t =-0.47, p =.68 & t =-0.17, p =.57,). For patients 3 and 4, who both had PSP for 4 years, the difference between sessions was more prominent ( t =1.29, p =.10 & t =3.19, p =.002,). Patient 5, with a disease duration of 6 years, also showed a significant difference ( t = 2.94, p =.008). The latter two patients showed strikingly large differences in mean sentence completion time under tDCS compared to the sham session (4472 vs. 5664 ms & 2637 vs. 5286 ms). Conclusion Our results show that tDCS can improve sentence completion performance in PSP. Based on the statistical analysis for individual patients, a connection between the duration of illness and the effectiveness of tDCS seems possible. Since tDCS studies mostly have small or medium effect sizes, more patients with comparable disease duration need to be studied. But on the individual level, the results are promising. In addition, further influences should be investigated such as other language tasks, gender, and educational factors.