This study evaluated the 12-month follow-up results and costs of a personalized, medical office-based intervention focused on behavioral issues related to dietary self-management. Two hundred and six adults having diabetes attending an internal medicine outpatient clinic visit were randomized to either Usual Care or to Brief Intervention. The single session intervention involved touchscreen computer-assisted assessment that provided immediate feedback on key barriers to dietary self-management, goal setting and problem-solving counselling. Follow-up components included phone calls and videotape intervention relevant to each participant. Brief Intervention produced significantly greater improvement than Usual Care on multiple measures of change in dietary behaviour (e.g., covariate adjusted difference of 2.2% of calories from fat; p = 0.023) and on serum cholesterol levels (covariate adjusted difference of 15 mg/dl; p = 0.002) at 12-month follow-up. There were also significant differences favouring intervention on patient satisfaction (p < 0.02) but not on HbA1c levels. The costs of intervention ($137 per patient) were modest relative to many commonly used practices.