Stress is known to negatively affect health and is a potentially serious barrier to diabetes-related health outcomes. This paper synthesizes what is known about stress and glycemic control among people with type 1 and type 2 diabetes across the lifespan. Chronic stress-especially in relation to living with diabetes-was most strongly associated with A1c, particularly among subgroups that face disproportionate stress, such as minority groups or adolescents/young adults. Mechanisms of the stress-A1c association include physiological, psychological, behavioral, and environmental links. Understanding the dimensions of stress as they relate to health in diabetes can be of significant clinical importance, and interventions targeting mechanisms that either exacerbate or buffer stress have reported modest improvements in A1c.