A randomised controlled trial to determine the acceptability to dentists and patients of cavity preparation with an Erbium:YAG laser as compared with conventional handpieces.Fifteen dentists (9 GDPs, 1 community dentist and 5 hospital dentists) treated 77 patients (age range 3.5-68 years old) who had two matched cavities, in a split mouth, randomised trial. One cavity was prepared conventionally, the other with the laser, with dentist and patient preference determined by questionnaire.In the majority of cases, where dentists expressed a preference, it was for conventional cavity preparation, and this was significant (P or = 10 years who expressed a preference, preferred laser treatment, and this was significant (P or = 10 years old preferred laser treatment. Patients < 10 years old did not express a preference.