This investigation was designed to explore Yaqui Indian perceptions of mental disorder. Since little empirical work has been done regarding mental health issues among the Yaquis, this study attempted to provide exploratory descriptive data in this area. The investigation sought to address the following questions: How do the Yaquis describe someone with "mental problems"? Would they include culturally-specific descriptions? Would the Yaquis be able to classify or categorize "mental problem"? Would they differ from other groups in determining whether specific behavior patterns would be labeled "mental problems"? What kinds of help would be enlisted for persons described as having "mental problems"? A survey of three Tucson area Yaqui communities was undertaken using eight members of the Yaqui Health Program as interviewers. Eighty-one Yaquis (20 males and 61 females) responded to the survey (2.8 percent of the enrolled Yaquis in Pima County). The first part of the survey instrument consisted of eleven open-ended questions asking about mental disorder, its cause and treatments available. Five behavioral vignettes (Star, 1955) were also presented and respondents were asked questions about whether the behaviors described mental problems and what might be the causes of such behaviors. Elicited Yaqui descriptions of persons with mental problems were then given to three groups of five sorters each: Yaquis, low SES Anglos, and psychology M.A.'s. These groups were asked to sort the descriptions based on similarity of problem. The Yaquis were found to be relatively knowledgeable about available mental health services. Very few culturally-specific descriptions or folk beliefs were elicited. Respondents tended to identify social, environmental or psychological factors as causing mental problems. Also, with one exception, the Yaquis were found to be quite similar to other groups in labeling problem behaviors as mental problems. The Yaquis did not appear to classify mental problems in a culturally-specific way. It is suggested that interviewer effects may have contributed to these results and that the Yaquis may not be as assimilated as these results suggest.