In general, the prevalence of caries in African children may be classified as low to very low. In order to reduce this level even further, methods including the practice of good oral hygiene and administration of fluoride, e.g. water fluoridation, have been suggested. In 1984,1986 and 1988, a mixed-longitudinal study amongst schoolchildren was carried out in a rural and urban area of Tanzania. In the rural area, shallow wells had been constructed at different periods in time in eight villages since the late 1970s. The drinking water in three of the villages contained fluoride in the range of 0.5–0.8 ppm (fluoridated) and contained less than 0.4 ppm fluoride in the remaining five villages (non-fluoridated). These fluoride levels were disclosed to the authors only during the course of the study. Thus the data were reanalysed to investigate the effects of fluoride and length of fluoride exposure on caries experience in the deciduous dentition. The study was carried out amongst 522 7- and 8-year-olds. Fluoride tablets were not used and toothpaste was virtually unavailable. Three periods of fluoride exposure were identified, i.e. 3,5 and 7 years. The outcome variable was the mean dmft score in deciduous molars whereas the explanatory variables were age, length of fluoride exposure and year of investigation. Nutrition was considered a co-variate. Analysis of co-variance revealed a fluoride effect (p = 0.0004). Regression analysis did not show significant relationships between the mean dmft score and the three periods of fluoride exposure. The findings indicated that 3 years’ exposure to low fluoride levels in drinking water can reduce further low caries severity levels in deciduous molars.