The neighbouring cantons Basel-Stadt and Basel-Landschaft had introduced different fluoridation schemes for caries prevention: Basel-Stadt provided drinking water fluoridated at 0.8-1 ppm F since 1962, while Basel-Landschaft introduced fluoridated domestic salt (250 ppm F since 1983). Representative samples of 12-year-old schoolchildren (6th-graders) were studied to evaluate the prevalence of (I) dental fluorosis (FOP) using the Thylstrup-Fejerskov (TF) index, (II) non fluoride-associated enamel opacities (non-FOP), and (III) hypoplasia of the incisors. Standardised frontal colour photographs were taken and assessed by four examiners after projection. Of 373 schoolchildren studied in 1999 in Basel-Stadt 119 (31.9%) showed fluoride-associated enamel opacities, i. e. 66 (17.7%) a very mild form (TF score 1), 47 (12.6%) a mild form (TF score 2), five scored TF3 and one TF5. In addition, non-FOP were diagnosed in 115 (30.8%) and hypoplasia in 47 (12.6%) children. Among the 448 children evaluated in 2001 in Basel-Landschaft 143 (31.9%) showed FOP, namely 74 (16.5%) scored TF1, 54 (12.2%) scored TF2, 12 (2.7%) scored TF3, and three (0.7%) scored TF5. Non-FOP were found among 93 (20.8%) and hypoplasia among 56 (12.5%) children. Thus, in spite of different fluoridation schemes in the two cantons, the prevalences of FOP were identical. Most fluoride-associated enamel opacities were mild or very mild. They did not represent an aesthetic problem and certainly not a public health concern.