Precursor behaviors are innocuous behaviors that reliably precede the occurrence of problem behavior. Intervention efforts applied to precursors might prevent the occurrence of severe problem behavior. We examined the relationship between precursor behavior and problem behavior in three individuals with developmental disabilities. First, a descriptive (correlational) assessment focusing on transitional probabilities, which established that problem behavior typically followed precursor behavior, was conducted. Next, a functional (experimental) analysis was conducted to evaluate the relationship between precursor and problem behavior. Results suggested that these two behaviors served the same function. Finally, in the intervention phase, participants were taught a response that was functionally equivalent to the precursor behavior. Results demonstrated a decrease in the frequency of problem behavior. Collectively, these results suggest that prevention efforts might profitably be focused on precursor behavior. Further implications for the use of functional analysis and functional communication training in prevention are discussed. (Contains 2 tables and 2 figures.)