The frequency of self-reported high pesticide exposure events (HPEE) has been recorded in the NCI/EPA/NIEHS Agricultural Health Study (AHS). Fourteen percent (14%) of the enrolled applicators responding reported "an incident or experience while using any pesticide which caused an unusually high exposure." These data show, as expected, that the probability of a report of an HPEE increases with the cumulative number of days of pesticide application reported by the applicator. We have developed a three-parameter model that predicts the risk odds ratio (OR) of an HPEE as a function of the number of days that pesticides are applied. These events are costly in terms of resulting health-care visits, lost time from work, and potential risk for cancer and other chronic diseases. We propose that failure to carefully follow all the pesticide manufacturer's label requirements, inexperience, and random events (i.e., breaking hose) are the three factors responsible for the events observed. Special precautions for new or infrequent users of pesticides are indicated.