Coronary artery calcium (CAC) has been previously associated with atherosclerotic plaque disease and coronary events. Thus, identifying predictors of CAC progression may provide new insights for early risk-factor intervention and subsequent reduction of the rates of more severe atherosclerotic disease. The aim of this study was to identify risk factors for CAC progression and evaluate whether risk-factor change was related to CAC progression in a cohort of patients with type 1 diabetes mellitus (DM). Participants in the Pittsburgh EDC Study, a prospective investigation of childhood-onset type 1 DM, who underwent 2 electron beam tomographic screenings 4 years apart were selected for study (n = 222). CAC was calculated using the Agatston method of scoring, and progression was defined as an increase >2.5 in the square root-transformed CAC score. Adjusting for DM duration and initial CAC score, body mass index (BMI; odds ratio [OR] 1.13, 95% confidence interval [CI] 1.01 to 1.26), non-high-density lipoprotein cholesterol (OR 1.01, 95% CI 1.003 to 1.03), and albumin excretion rate (OR 1.30, 95% CI 1.03 to 1.63) were associated with CAC progression. When considering change in risk factors, an increase in BMI (OR 1.38, 95% CI 1.10 to 1.72) was also associated with CAC progression after adjustment. In conclusion, in this cohort with type 1 DM, in addition to baseline BMI, non-high-density lipoprotein cholesterol, albumin excretion rate, and all known coronary artery disease risk factors, weight gain further added to the prediction of CAC progression. Thus, weight control, in addition to lipid and renal management, may help retard atherosclerosis progression in persons with type 1 DM.