The caries increment (filled surfaces) from the ages 7 to 15 years were compared in children with three or fewer (low prevalence group) or eight or more filled surfaces (high prevalence group) at the age of 8. The children participated in a fortnightly fluoride mouthrinsing program (10 ml of 0.2% NaF). Following 8 years of dental treatment and caries prophylaxis, the caries increments were 11.4 (s.d. = 7.7, n = 23 subjects) and 17.1 (s.d. = 9.6, n = 39 subjects) surfaces, i.e. significantly different (t = 2.376). Significantly (t = 4.034) more fillings had been required in the high than in the low prevalence group (31.1 +/- 17.1 vs. 15.5 +/- 9.6). The "risk group" could be identified at the ages of 7 to 8 by high caries prevalence and high ratio fillings/caries increment. Social class and number of teeth accounted more for the initial caries prevalence than for the caries increment. Correlation analyses revealed a significant, but not strong (r = 0.50), association between caries prevalence at the age of 7 and increment of fillings.