The purpose of the present study was to examine the demographic, medical, and social cognitive determinants of exercise intentions in a institution-based cohort of primary brain tumor patients. Using a cross-sectional survey, 100 primary brain tumor patients completed a mailed survey that assessed medical and demographic characteristics, past exercise behavior using the Godin Leisure Time Exercise Questionnaire (GLTEQ), and social cognitive beliefs towards exercise using Aizen's theory of planned behavior (TPB; i.e. intention, perceived behavioral control, subjective norm, affective and instrumental attitude). Descriptive statistics indicated that participants had positive social cognitive beliefs towards exercise. In support of the tenets of the TPB, we found moderate to large (>0.40) positive correlations between the majority of TPB constructs. Moreover, the TPB constructs combined to explain 32% of the variance in exercise intentions with affective attitude (beta = 0.24; p = 0.020) and perceived behavioral control (beta = 0.36; p<0.001) being the most important determinants. Except past exercise behavior, medical and demographic variables were not consistently correlated with any TPB constructs. Finally, participant's gender and body mass index influenced the association between instrumental attitude and exercise intention with male and overweight/obese patients (> or =25 kg/m(2)) considering the health benefits of exercise to be more important than their female and normal weight (<25 kg/m(2)) counterparts. Information gained from this study suggests that the TPB is a useful framework to design and implement theoretically based interventions to promote exercise in primary brain cancer patients.