This study involves the development and initial validation of a questionnaire measuring the propensity for sexual inhibition and excitation in men: the Sexual Inhibition Sexual Excitation Scales (SIS/SES). The underlying theoretical model postulates that sexual response and associated behavior depend on dual control mechanisms, involving excitatory and inhibitory neurophysiological systems. The scales and their discriminant and convergent validity and test-retest reliability are described. In a sample of 408 sexually functional men (mean age = 22.8 years), factor analyses identified three higher-level factors: two related to sexual inhibition and one to sexual excitation. Multigroup Confirmatory Factor Analyses revealed that the factor structure provided an acceptable fit to the data obtained in a second (N = 459; mean age = 20.9 years) and third (N = 313; mean age = 46.2 years) sample of men, with similar distributions and relationships with other measures. Theoretical issues and areas for further research, including male sexual dysfunction and risk taking, are discussed.