Background. Sitting balance and the ability to perform selective trunk movements are important predictors of functional outcome after stroke. However, studies evaluating the effect of exercises aimed at improving trunk performance are sparse. Objective. To examine the effect of additional trunk exercises on trunk performance after stroke. Methods. An assessor-blinded randomized controlled trial was carried out at an inpatient stroke rehabilitation center. In total 33 participants were assigned to an experimental group (n = 17) or a control group (n = 16). In addition to conventional therapy, the experimental group received 10 hours of individual and supervised trunk exercises; 30 minutes, 4 times a week, for 5 weeks. Trunk performance was evaluated by the Trunk Impairment Scale (TIS) and its subscales of static and dynamic sitting balance and coordination. A general linear repeated measures model was used to analyze the results of our study. Results. No significant differences were found pretreatment between the 2 groups for the collected demographic variables, stroke-related parameters, clinical measures, number of therapy sessions received, and primary outcome measure used. Posttreatment, a significantly better improvement was noted in the experimental group compared to the control group for the dynamic sitting balance subscale only; measuring selective lateral flexion initiated from the upper and lower part of the trunk, (P = .002, post hoc power calculation = .90, effect size = 1.16). Conclusions. Our results suggest that, in addition to conventional therapy, trunk exercises aimed at improving sitting balance and selective trunk movements have a beneficial effect on the selective performance of lateral flexion of the trunk after stroke.