The aim of the present study was to evaluate the prevalence of self-reported problems (fear, pain, unpleasantness, fainting) of dental and medical injections, and the extent to which such problems may lead to avoidance of necessary treatment. The study included a representative sample (n = 1385) of 18-yr-old students attending high schools in the county of Hordaland, Norway. Data were collected by use of questionnaires completed in the classrooms. More problems were reported during dental than medical injections. About 17% and 15% of participants reported high fear during their last dental and medical injection, respectively. Fainting had been experienced by 2% during a dental injection and by 7% during a medical injection. Avoidance of treatment when an injection is needed was 6.7% for dental treatment and 5.2% for medical treatment. In multiple regression analyses, fear was the only explanatory factor for the avoidance of dental treatment. It is concluded that self-reported problems of injections are prevalent in this age group, particularly among girls, and that it may lead to the avoidance of necessary treatment in 5-7% of the adolescent population.