The authors prospectively assessed the causal relationship between psychosocial factors and glycemic control in 256 Japanese outpatients with Type 2 diabetes. Using structural-equation modeling, they first developed a causal model in which glycosylated hemoglobin (HbA(1c)) at 6 months after assessment was influenced by the baseline psychosocial factors. Then, the reliability of the causal model was investigated with measurement of HbA(1c) at 12 months after baseline. Self-efficacy directly reinforced adherence, and adherence had a direct association with future HbA(1c). Other psychosocial factors, including social support, diabetes-related distress, daily burden, and emotion-focused coping prospectively influenced HbA(1c) indirectly through self-efficacy.