On December 8, CDC issued a Health Alert Network health advisory to notify health care providers and the public about an outbreak of RMSF among people in the United States with recent travel to or residence in the city of Tecate, state of Baja California, Mexico. RMSF is a severe, rapidly progressive, and often deadly disease transmitted by the bite of infected ticks, although many patients do not recall being bitten by a tick. Doxycycline is the treatment of choice for patients of all ages. As of December 8, five patients have been diagnosed with confirmed RMSF since late July 2023; all had travel to or residence in Tecate within two weeks of illness onset. RMSF is endemic in multiple border states in northern Mexico, including but not exclusive to Baja California, Sonora, Chihuahua, Coahuila, and Nuevo León. Healthcare providers should consider RMSF in their differential diagnoses of patients who have reported recent travel to Tecate, Mexico, or other areas of northern Mexico and subsequently develop signs or symptoms of an unexplained severe febrile illness. Consider initiating doxycycline based on presumptive clinical and epidemiologic findings, and do not delay treatment pending the result of a confirmatory laboratory test.