Because restaurants routinely serve food with more calories than people need, dining out represents a risk factor for overweight, obesity, and other diet-related chronic diseases. Most people lack the capacity to judge the caloric content of food and there is limited evidence that people make use of calorie-labeling information when it is available. Standardized portion sizes would not preclude people from eating as much as they want, but would make the amount they are getting fully transparent. We describe the potential benefits and means of implementing a system of standardized portion sizes that might facilitate a healthier diet among the US population.