Objectives: The growing body of evidence suggesting that lifestyle changes and aggressive medical management reduce the risk of strokes in patients with carotid stenosis has fostered interest in noninvasive screening. The objective of this study was to develop recommendations for follow-up carotid ultrasound surveillance of patients with < 60% carotid stenosis.; Methods: This retrospective observational cohort study includes 2956 patients seen between August 1998 and March 2015 in 4440 visits. Data analysis was restricted to 7710 carotid ultrasounds. Primary outcome was progression of carotid stenosis as defined by the "bulb" method: baseline stenosis of 0%-39% progressed to 40%-59% on subsequent examination, baseline stenosis of 0%-39% progressed to >= 60%, or baseline of 40%-59% progressed to >= 60%. Progression was estimated using Cox proportional hazard ratios and the Kaplan Meier method.; Results: More than 10% of patients progressed in the 40%-59% baseline group within 12 months compared to 78 months for the 0%-39% baseline group. Patients who progressed had a higher proportion of peripheral vascular disease, and current/former smoking compared to those who did not. While there were statistically significant correlations between medication classes and comorbidities, none of the medications studied appeared to slow carotid stenosis progression.; Conclusions: In our experience, for patients with a 0%-39% carotid stenosis, follow-up examination should be performed at 6-year intervals. For patients with 40%-59% carotid stenosis, follow-up should be obtained annually to identify those who progress to a level requiring intervention. Future studies should examine whether study findings can be replicated using other approaches for determining carotid stenosis.