Background: Few previous randomized trials investigated whether additional therapies could improve the efficacy of the standard combined-approach (stuttering modification and fluency shaping) treatment in adults who stutter (AWS). Aims: To evaluate in a randomized controlled clinical trial whether the addition of a psychomotor therapy over a standard combined-approach treatment could improve the efficacy of treatment in young AWS. Methods & Procedures: A total of 47 young AWS (mean age = 24 years, 79% males) with at least moderate stuttering (evaluated by the stuttering severity instrument--3, SSI-3 [greater than or equal to] 21 points) were randomized to either a standard combined-approach treatment (24 AWS, control group, 16 sessions of 40 min over 8 weeks) or to standard treatment plus the psychomotor therapy (23 AWS, intervention group, adding 20 min of psychomotor training after each session). Stuttering improvement was assessed by reductions in SSI-3 scores, examined using Wilcoxon tests. The primary outcome was the difference in SSI-3 reductions between the control and intervention groups, evaluated by Mann-Whitney tests. Outcomes & Results: Control and psychomotor intervention groups were well-balanced in most baseline characteristics, including stuttering severity (mean SSI-3 score = 32.6 points). After treatment both groups significantly reduced SSI-3 (mean absolute reduction = 10.1 points, 95% confidence interval (CI) = 8.5-11.7 points, p < 0.001), without any significant difference between the two groups (mean difference = 1.0 point, 95% CI = -2.2 to -4.2 points, p = 0.39). Also, there were no significant differences between the groups in relative percentage reductions, or in the proportion of individuals who reached a > 30% reduction or a post-treatment SSI-3 < 20 points. There were also no significant differences in separate SSI-3 components (frequency and duration of stuttering events and physical concomitants). Conclusions & Implications: This randomized controlled trial did not demonstrate any benefit of adding a psychomotor therapy over a standard combined-approach treatment in young AWS.