This study used an ABCB within-subjects design to examine the relative effects of feedback and prompts on safe sitting posture. Participants were three office workers. The dependent variables were the percentages of time the participants spent in four safe individual body positions and in the safe overall sitting posture. After baseline (A), feedback (B) was introduced, and prompts (C) were introduced in the next phase. In the final phase, feedback (B) was reintroduced. Results indicated that sitting postures improved substantially when feedback was provided. However, the prompts had only limited effects on the sitting posture. Thus, the use of a combined antecedent-based and consequence-based intervention is advised to improve sitting posture. (Contains 1 table and 2 figures.)