Male sexual dysfunction (MSD) and female sexual dysfunction (FSD) may be of multifactorial etiology; rating these disorders heretofore has been based on subjective, patient-reported criteria. This article discusses the process of determining sexual disability by incorporating objective, laboratory-based data in order to render more reliable and valid determinations, including whether the patient has received appropriate treatment and is at maximum medical improvement. MSD is of organic, psychogenic, mixed, or indeterminate cause, and identification of specific MSD etiology can be made via a thorough sexual and medical history, physical examination, and tailored laboratory testing. Routine laboratory studies should include complete blood count, serum chemistry, lipid profile, and serum free/total testosterone and prolactin levels. Using the history and physical examination and laboratory studies, evaluators can differentially diagnose more than 80% of patients as having either organic or psychogenic MSD. Objective laboratory studies for MSD include nocturnal penile tumescence, duplex Doppler ultrasound, and neurosensory testing. FSD is a prevalent, age-related women's health issue that reportedly affects up to half of women older than 50. FSD evaluation requires a comprehensive sexual and medical history as well as physical examination, pelvic examination, hormonal profile, and an evaluation by a sex therapist. Laboratory testing is not yet fully defined but may include measurements of genital blood flow, vaginal pH and compliance, and genital vibratory sensory threshold determination.