It is important to determine the sexual interests of those accused of child molestation. Visual reaction time and plethysmography are two means of measuring sexual interest with some objectivity, but there has been no direct comparison of these methodologies. The reliability and validity of visual reaction time and plethysmography were evaluated in groups of individuals with sexual interest in children of various ages and genders. Results showed that both methods of assessment had a high reliability and validity. Visual reaction time has the added advantages that it can be used without nude slides and is a briefer assessment.