It has been shown that dental erosion is not a very rare condition. Careful observation and clinical experience led us to hypothesize a progression of these lesions with time despite dietary counselling and oral hygiene instruction. The purpose of this study was to determine the progression rate and risk factors of dental erosion and wedge-shaped defects over a 6-year period. In the year 1987, 204 randomly selected persons living in Bern from two age groups (26-30 and 46-50 years) were examined for frequency and severity of dental erosion and wedge-shaped defects. In the year 1993, 55 persons could be re-examined by the same dentist using the same indices. Further, detailed case histories of the patients were recorded and the flow rate and buffering capacity of the saliva were determined. The results indicated a distinct progression of erosion on facial and occlusal surfaces and wedge-shaped defects over the 6-year period. The increase in the defects was more marked in the older age group. Surprisingly, nutritional habits did not change despite thorough informative discussion about erosive foodstuff with every patient during the first session. Multiple linear regression analysis revealed consumption of nutritional acids and age as significant risk factors explaining 28% of the variability of the progression of erosions. The significant factors for the progression of wedge-shaped defects were identified to be frequency of tooth brushing and age, explaining 21% of the variability of the progression of wedge-shaped defects. In summary, there was a definite statistically significant progression of non-carious dental hard tissue defects in our sample. This progression was correlated with age (erosion and wedge-shaped defects), consumption of dietary acids (erosion) and frequency of toothbrushing (wedge-shaped defects).