Although the anti-caries effects of standard fluoride (F) toothpastes are well established, their use by preschoolers (2- to 5-year-olds) has given rise to concerns regarding the development of dental fluorosis. Thus, a widespread support of low F toothpastes has been observed. The aim of this study was to assess the effects of low (<600 ppm) and standard (1,000-1,500 ppm) F toothpastes on the prevention of caries in the primary dentition and aesthetically objectionable (moderate to severe) fluorosis in the permanent dentition. A systematic review of clinical trials and meta-analyses were carried out. Two examiners independently screened 1,932 records and read 159 potentially eligible full-text articles. Data regarding characteristics of participants, interventions, outcomes, length of follow-up and potential of bias were independently extracted by two examiners and disagreements were solved by consensus after consulting a third examiner. In order to assess the effects of low and standard F toothpastes on the proportion of children developing caries and fluorosis, pooled relative risks (RR) and associated 95% confidence intervals were estimated using a fixed and a random-effects model, respectively. Five clinical trials fulfilled the inclusion criteria. Low F toothpastes significantly increased the risk of caries in primary teeth [RR = 1.13 (1.07-1.20); 4,634 participants in three studies] and did not significantly decrease the risk of aesthetically objectionable fluorosis in the upper anterior permanent teeth [RR = 0.32 (0.03-2.97); 1,968 participants in two studies]. There is no evidence to support the use of low F toothpastes by preschoolers regarding caries and fluorosis prevention.