Specific genetic syndromes affect individuals' sexual development, experiences, and fertility. Individuals with specific syndromes can also display inappropriate sexual behavior resulting from vulnerabilities presented by their genetic makeup. Using clinical case studies, we discuss the specific impact that Down, Prader–Willi, and Williams syndromes can have on sexual development and behavior. Applying a biopsychosocial approach, we present the primary sexual effects, such as delayed sexual development and infertility. These genetic syndromes are also associated with challenges that are not specifically sexual in nature but that affect sexual expression, such as self-injury, mental health issues, or epilepsy. Medication side effects are also discussed. We conclude with treatment recommendations for individuals with sexual challenges, considering the unique effects of these three syndromes on sexuality.