Abstract Objective. To evaluate the effect of milk supplemented with fluoride and/or probiotic bacteria on primary root caries lesions (PRCL) in older adults. Materials and methods. After informed consent, 160 healthy subjects, 58-84 years of age, with at least two PRCL were recruited and randomly assigned to one of four parallel study groups drinking 200 ml milk once daily for 15 months. Group A consumed standard milk (placebo); Group B ingested milk supplemented with 5 ppm F and probiotic bacteria (Lactobacillus rhamnosus LB21, 10(7) CFU/mL); Group C drank milk with only probiotic bacteria and group D milk contained only fluoride. Primary endpoints were Root Caries Index (RCI) and electric resistance measurements (ECM) carried out by one blinded single examiner. Secondary endpoints were mutans streptococci and lactobacilli counts in saliva and plaque estimated with chair-side tests. Data were compared within and between groups with non-parametric tests. Results. The drop out rate was 38%. At baseline there were no statistical differences between the groups. Significantly higher numbers of RCI reversals were found in groups B, C and D compared with group A (p <0.05). The mean ECM values increased significantly (p <0.05) in all groups except for the placebo group A, indicating that remineralization occurred. The effect was most beneficial in the two groups that contained fluoride. No significant alterations were displayed regarding the microbial counts. No severe adverse effects were reported during intervention. Conclusion. Daily intake of milk supplemented with fluoride and/or probiotic bacteria may reverse soft and leathery PRCL in older adults.