On 1 January 1996, diphtheria-tetanus revaccination at the age of 5 years was implemented in the Danish Childhood Vaccination Programme. Initially, a combined DT vaccine containing 25 Lf diphtheria toxoid was used. Due to a high frequency of spontaneously reported adverse reactions, however, concerns were raised that the diphtheria dose was too high, and it was reduced to 6.25 Lf. This survey presents the rates of spontaneously reported adverse reactions following diphtheria-tetanus revaccinations of 4-6-year-old from 1996 to 2002. The change to the lower dose of diphtheria toxoid resulted in a remarkable reduction in the yearly rates of injection site reactions: in 1996, the rate was 180 injection site reactions per 100,000 vaccinations; from 1998 to 2002, this changed to between 12 and 24 reactions per 100,000 vaccinations. Furthermore, the rates of systemic reactions such as fever were reduced.