Oral leukoplakia is a relatively common oral lesion that, in a varying proportion of cases, undergoes malignant transformation. The aim of this review was to assess the effectiveness of treatments for leukoplakia. Randomized controlled trials (RCTs) enrolling patients with a diagnosis of oral leukoplakia were identified by searching biomedical databases, hand-searching relevant oral medicine journals, and contacting oral medicine experts through a European mailing list. The methodological quality of included studies was assessed on the basis of the method of allocation concealment, blindness of the study, and loss of participants. Data were analyzed by calculating relative risk. Malignant transformation of leukoplakia, demonstrated by histopathological examination, was the main outcome considered. Secondary outcomes included clinical resolution of the lesion and variation in dysplasia severity. Six RCTs were included in the review. Vitamin A and retinoids were tested in four RCTs; the other agents tested were bleomycin, mixed tea, and beta carotene. Malignant transformation was recorded in just two studies: none of the treatments tested showed a benefit when compared with placebo. Treatment with beta carotene and vitamin A or retinoids was associated with better rates of clinical remission, compared with placebo or absence of treatment. Whenever reported, a high rate of relapse was a common finding. Side effects of variable severity were often described; however, interventions were well accepted by patients since drop-out rates were similar between treatment and control groups. It is noteworthy that the possible effectiveness of surgical interventions, including laser therapy and cryotherapy, has apparently never been studied by means of an RCT. To date, in conclusion, there is no evidence of effective treatment in preventing malignant transformation of leukoplakia. Treatments may be effective in the resolution of lesion; however, relapses and adverse effects are common.