The purpose of the present study was to assess the progression rate of approximal carious lesions in Norwegians aged 14-18 years. Sixty-five subjects whose average age at base line was 14.9 years had one pair of posterior bitewing radiographs taken annually from 1982 to 1986. One examiner assessed all radiographs in chronologic order, recording degree of approximal caries. When a surface changed from one state to another, it was assumed to have changed at the midpoint between the two examinations. A total of 590 lesions were observed. Uncensored lesions took on average nearly 3 years to penetrate the enamel. Inclusion of right censored lesions by the Kaplan-Meier approach increased the uncensored estimate by approximately 20%. The average for doubly censored lesions was about 6.5 years. Low average rate of caries progression coupled with wide variations between lesions and among subjects suggests a need for individually prescribed recall routines.