A great discrepancy exists between the potential number of adult basic education (ABE) participants (all adults who have not graduated from high school) and those who actually choose to participate in ABE. To determine why high school dropouts choose not to participate in ABE, telephone interviews were conducted with a carefully constructed, statewide sample of 129 adults in Iowa who were eligible for ABE but had never participated. During the interviews, respondents were asked to rate the accuracy of 32 statements describing reasons for not taking classes to complete high school. (The statements were derived from earlier interviews with ABE nonparticipants.) The ratings were subjected to factor analysis, which suggested that there are four basic reasons why eligible adults choose not to participate in ABE: low perception of need; situational barriers; perceived effort; and dislike for school. Older adults were most likely to have low perceptions of need, whereas situational barriers most often prevented participation of young, married adults who were employed full time and had children. The study concluded that adult educators should try to change perceptions of potential students toward education, admit that low perception of need may be reasonable in some cases, and work toward removing situational barriers by providing child care and other support services. (KC)