OBJECTIVES: This study reports changes in non-cavitated tooth surface diagnoses after a 4-year period. METHODS: Dental examinations were conducted for Iowa Fluoride Study cohort children who had non-cavitated lesions in the primary dentition and were also examined an average of 4 years later in the mixed dentition. Comparison of fluoride exposures, socioeconomic factors, and beverage consumption patterns were made between children who had lesions progress and those who did not. RESULTS: Of 129 non-cavitated pit and fissure lesions in the first exams, 40 (31%) progressed to either frank decay or filled status, while among 132 noncavitated smooth surface lesions, 7 (5%) were filled and none had frank decay in the second exam. No fluoride, socioeconomic status or beverage variables were significantly associated with lesion progression. CONCLUSIONS: Non-cavitated smooth surface lesions rarely progressed in this age group, but nearly one-third of pit and fissure lesions progressed.