Overweight and obesity constitute a significant US public health issue and particularly disturbing is the accelerating disparity among ethnic groups. Mexican Americans have displayed an alarming increase in weight for height status over the past two decades (Hedley et al., 2004). Notably, the prevalence of overweight and obesity among female Mexican Americans aged at least 20 years is now 69 percent and 37 percent respectively (National Center for Health Statistics, 2004). Weight reduction strategies include a combination of diet and physical activity; however, identification of factors associated with activity participation must precede development of effective physical activity interventions. The theory of planned behavior has been applied in studies of exercise determinants among adults. This theory includes the domains of attitude, subjective norm, and perceived behavioral control and posits that individuals will intend to perform behavior when they evaluate it positively, believe that important others think they should perform it, and perceive it to be under their control (Ajzen, 1991). Therefore the purpose of the present investigation was to extend research using the theory of planned behavior in predicting physical activity intention to female Mexican Americans. The sample was drawn from those parents, legal guardians, and adult relatives/friends present during registration for a child educational program held on the University of Texas-Pan American campus. Data were gathered through a self-report survey instrument, in both English and Spanish, dealing with physical activity level, attitudes, perceived behavioral control, and subjective norm variables as well as age, gender, and education descriptors. Two hundred one females (M age=37.2 years, SD=6.81; age range 24 to 66 years) served as study subjects. Results indicated Ss held a positive attitude toward physical activity, believed that important others think they should be active, and felt they possessed the ability to do so. Hierarchical analyses revealed that perceived behavioral control (14% of the variance; r=.382, p<.001) made the greatest contribution to the prediction of intent to be physically active. Findings suggest that interventions for promoting increased physical activity among the population group studied foster a sense of control over physical activity situations, particularly internal perceptions of control or self-efficacy. Keyword(s): adult fitness, diversity, exercise/fitness