Objective: The primary aim of this project is to assess the progression rates from baseline of initially identified inter-proximal early carious lesions at 2 years and 4 years. A secondary aim is to determine if factors such as age, number of lesions, and receipt of preventive interventions predict caries progression. Methods: This study utilized data from a chart audit of members receiving dental care from the HealthPartners Dental Group. Potential subjects were identified from electronic data from 1996-2000 utilizing the criteria of having a routine dental examination at baseline, 2 and 4 years. Subjects' charts were examined to identify one or more carious lesion and determine if radiographs are present at baseline, 2 and 4 years (window of 6 months). A trained and calibrated dental hygienist gathered data on lesion depth at baseline, and 2 and 4 years, age and receipt of preventive treatment. Results: Data on 260 lesions were collected from 96 individuals. At 2 years 41% of the lesions had progressed, and 80% had progressed at 4 years (p<.01). The average depth change of lesions that progressed was very modest (Median = 1 unit). Age, number of lesions and receipt of preventive treatment did not predict progression. A very large person-level intra-class correlation (ICC=.31) indicated that factors varying across individuals are related to progression. Conclusions: These results help quantify the progression risk of early carious lesion. When lesions progress, the change in size is generally modest. Holding off on restorative treatment and utilizing remineralization therapy to arrest or reverse early carious lesions is an appropriate and low risk approach for many dental patients. Dental providers should also look at individual caries risk when determining the risk of caries progression. Supported by HPRF, internal grant #00-028.