The purpose of this study is to evaluate the effects of "Picture Exchange Communication System" (PECS) training, using a multiple baseline design on the independent initiations of three adults with developmental disabilities and severe communication deficits. All participants increased their independent initiations, although at different levels of quality and quantity throughout PECS training. Results demonstrate a functional relationship between the teaching of PECS and the increase of independent initiations, and these independent initiations continued to improve after initial training. In addition, problem behaviors (off-task and tantrum behaviors) were monitored to assess the collateral effects of PECS training. Results of data collection on untreated problem behaviors showed marked decreases, especially in the last half of PECS training, and remained below baseline levels during follow-up. The results of this study suggest that participants taught via PECS increased their initiation of requests, thereby increasing their independence and choice making, which also appears to have collateral effects on problem behaviors. This study extends the literature on PECS training with adults with developmental disabilities and severe communication deficits by demonstrating that at least one of the participants learned all six phases. This study also demonstrates collateral changes in untreated problem behaviors in this adult population.