A split mouth clinical trial was undertaken to compare the retention of fissure sealants placed using laser or acid conditioning. After a mean follow-up period of 14.5 months, the retention rate for laser conditioning was greater than that for acid etching (97.9 per cent versus 94.6 per cent, respectively), although this difference was not statistically significant. No adverse effects occurred during or subsequent to laser conditioning procedures. It is concluded that carbon dioxide laser conditioning is a viable alternative to acid etching for fissure sealing.