This prospective, in vivo study compared bond failure and enamel decalcification with a cyanoacrylate bracket bonding system (SmartBond, Gestenco International, Gothenburg, Sweden) and a traditional light-cured composite system (Light Bond, Reliance Orthodontic Products, Itasca, Ill). A total of 327 teeth were evaluated after a period of 12 to 14 months; 163 experimental teeth were bonded with the cyanoacrylate bonding system, and 164 control teeth were bonded with the light-cured composite resin. All teeth were evaluated for breakage (bond failure). The average percentage of bracket failures with cyanoacrylate was 55.6% compared with 11.3% with composite resin (P <.001). All maxillary anterior teeth (94) were evaluated for enamel decalcification on a graded scale. Occurrence of enamel decalcification between the 2 bonding systems after 1 year of orthodontic treatment was similar. The cyanoacrylate bonding material had more than 4 times as many bond failures and a similar amount of decalcification as the traditional composite material. Cyanoacrylate as a routine orthodontic bonding agent is not a suitable bonding material for clinical practice at this time. It is important to test new bonding systems in vivo in several studies before using them in routine clinical practice.