Use of the CO(2) laser (λ = 10.6 μm, continuous wave, defocused) is an established procedure for the treatment of premalignant lesions. Through employment of the sp-mode as well as scanners, thermal laser effects can be reduced but, on the other hand, a lesser degree of destruction of dysplastic cells could lead to an increased recurrence rate. The purpose of this study was to prospectively evaluate the recurrence rates resulting from different methods of CO(2) laser vaporization. From May 1995 to May, 2005, 145 patients with a total of 148 premalignant lesions of the oral mucosa were treated in a prospective clinical study. Sixty-two lesions in 62 patients were vaporized with the defocused CO(2) laser (group 1). In a further 45 lesions (43 patients, group 2), a scanner was additionally employed. In the remaining 41 lesions (40 patients, group 3), vaporization was carried out in the sp-mode in which the scanner was also used. In September, 2005, recurrence rates in the three groups were evaluated. Use of the scanner in sp-mode resulted in the most irregular tissue vaporization. This can be accounted for by the irregular paths of the laser beam and the pulsed delivery of the laser energy. Statistically significant lowest recurrence rates were yielded by the defocused cw-technique followed by the cw-scanner and the sp-mode. These results indicate that for CO(2) laser treatment of premalignant lesions of the oral mucosa, the best results can be achieved with the defocused technique. It may be assumed that other methods with lesser penetration of thermal effects (e.g. sp, scanner) do not reach the deeper-lying cells and, consequently, render higher rates of recurrence.