The duty to warn genetically at-risk relatives of patients is one of the most misunderstood legal and ethical issues affecting clinical genetics. The legal doctrines are often associated with three state appellate court cases beginning in the mid-1990s. Since the HIPAA Privacy Rule went into effect in 2003, the duty to warn must be accomplished by warning the patient of the genetic nature of a diagnosed disorder or genetic risk and the necessity of warning at-risk relatives. Health-care providers are neither required nor permitted to warn at-risk relatives without the consent of their patients. Having warnings issued by the patient most closely aligns with traditional ethical principles and the interests of the parties. Physicians and other health-care providers can assist their patients by preparing jargon-free explanations of the genetic risk and offering consultation or referral services. In the future, the need for warnings is less likely to be triggered by diagnoses and more likely to be based on predictive information derived from genome sequencing and other technologies and data sources.