Half of the years of life lost in Latin America are attributable to chronic diseases. In Chile, despite a universal healthcare system and free medication for hypertension and diabetes, less than half of diagnosed patients have their disease under control. In a public healthcare system without fees it can be challenging to ensure patients appear for their scheduled appointments. In an attempt to improve appointment attendance, and ideally health, the ministry of health scaled-up an SMS appointment reminder program to all public primary care clinics in the country in 2015. My research this summer will evaluate the impact of this at-scale program on patient attendance and health.