The authors examined the influence of diet (dietary fat intake and dietary temperance) on relapse of patients with Crohn disease. A 1-year prospective study of 76 patients with Crohn disease was conducted. The criterion for eligibility was a Crohn Disease Activity Index score of 150 or lower for at least 1 month. The primary end point was defined as the relapse-free interval from the baseline until the first relapse. Fat intake was assessed using a validated diet history questionnaire. The degree of dietary temperance was assessed using a single-item nominal scale. The Cox proportional hazards model was used to evaluate the influence of diet. Crohn disease relapse was seen in 25 patients (33%), and 47 patients (62%) remained in continuous remission. A decreased ratio of n-6 polyunsaturated fatty acid (PUFA) to n-3PUFA (odds ratio = .38; p = .005) was associated with a poor prognosis. Dietary temperance also was significantly associated with prognosis (p = .014). More moderate dietary temperance decreased the risk of relapse (odds ratio = .22; p = .006). Effective prevention of relapse for Crohn disease patients might be achieved through moderate dietary temperance, particularly when the disease condition is unstable.