We conducted a sequence of two studies on the use of discrete-trial functional analysis and functional communication training. First, we used discrete-trial functional analysis (DTFA) to identify the function of problem behavior in three adults with intellectual disabilities and problem behavior. Results indicated clear patterns of problem behavior for each participant. Second, we used a modified multiple baseline design across participants to assess the effectiveness of functional communication training (FCT) on the acquisition of a replacement communicative response. We conducted postacquisition discrimination probes to evaluate the discriminated use of the new response. Results indicated that FCT was effective in producing acquisition and discriminated use of the replacement response for all participants. The study has relevance because of the empirical evidence of DTFA and its applicability to adults with intellectual disabilities.