Objective: The purpose of this study was to evaluate the effect of low-level laser therapy (LLLT) as an adjunct to standard therapy in acute pericoronitis. Methods: Eighty acute pericoronitis patients were randomly assigned to one of four LLLT groups: (neodymium: yttrium-aluminum garnet [Nd:YAG] 1064-nm: n = 20, 8 J/cm(2), 0.25W, 10 Hz, 10 sec; 808-nm diode: n = 20, 8 J/cm(2), 0.25W, continuous mode, 10 sec; 660-nm diode: n = 20, 8 J/cm(2), 0.04 W, continuous mode, 60 sec; or a placebo laser control group: n = 20). After standard treatment, LLLT or a placebo laser were applied to the treatment area at a distance of 1 cm from the buccal site. Interincisal opening, pain perception, and oral health-related quality of life (OHRQoL) were evaluated at baseline, 24 h, and 7 days after laser application. The data were analyzed by the one-way ANOVA test. Results: We found that the trismus and the OHRQoL in the Nd: YAG and the 808-nm diode groups were significantly improved when compared with the 660-nm diode and control groups at 24 h (p < 0.05). No statistically significant differences were detected on day 7 among the groups with regard to any of the parameters evaluated. Conclusions: The results demonstrate that both the 1064-nm Nd: YAG and the 808-nm diode lasers were effective in improving trismus and OHRQoL in acute pericoronitis. Taking into account the limitations of this study, we conclude that the 1064-nm Nd: YAG laser has biostimulatory effects and improves OHRQoL, making it suitable for LLLT.