This paper presents a viability study of the labial photoplethysmograph (LPG) in the physiologic assessment of female sexual function and investigates whether it would meet the requirements of a female sex offender assessment. Evaluation of physiologic components of female sexual responding is technically challenging and there are several limitations that present some unique challenges to forensic clinicians. The present study was designed to investigate the effectiveness of the LPG as a measure of female sexual arousal with a view to evaluating it as an analogous technique to phallometric testing for male sex offenders. Seventeen sexually healthy women were evaluated. General and genital physiological measurements were taken at baseline and in response to erotic and control stimuli. The correspondence between subjective appraisal of arousal and physiological responses was also undertaken. Findings indicated a clear and unequivocal measureable response to the sexual stimuli using the LPG but challenges remain and are discussed.