This study investigated the influence of internal surface treatment and margin location on the microleakage of 2 alumina-reinforced ceramic crown systems: In-Ceram (VITA Zahnfabrik) and Procera (Nobel Biocare). Full crowns were produced for each of the 2 systems (n = 24) in human premolars, with margins located in enamel and dentin, and luted with Single Bond and RelyX ARC (3M ESPE). Four internal ceramic treatments were tested: (1) aluminum oxide blasting (AO), (2) AO plus silane, (3) hydrofluoric acid etching (HF), and (4) HF plus silane. After thermal cycling, leakage was measured quantitatively. Statistical analysis (P < .05) showed higher leakage in dentin margins compared to enamel. In enamel, Procera showed greater leakage compared to In-Ceram. Generally, lower microleakage was observed for the AO plus silane treatment. Int J Prosthodont 2007;20:123–124.