Objective: To investigate the efficacy, tolerability, and long-term color stability of tooth whitening using two different bleaching techniques: an at-home tray technique (5.0% H2O2) and an over-the-counter strip technique (5.3% H2O2). Method and Materials: Thirty subjects were included in this two-cell, parallel, examiner-blinded, randomized clinical trial. Shade evaluations were performed with a value-oriented VITA shade guide. The null hypothesis was that there would be no differences between the groups and no improvements from baseline with regard to tooth shade. Bleaching sensitivity, gingival irritation, and patient acceptance were recorded on a visual analog scale (VAS). Scanning electron microscopy (SEM) was performed to detect any enamel surface changes. Results: After bleaching, both treatments demonstrated significant improvements in tooth shade (P .001 for both groups). At the 18-month recall, tooth shade remained significantly lighter than at baseline (P = .006 for tray group; P = .001 for strip group). However, a relapse of the tooth shade was observed compared with the immediate postbleaching result (P .05). VAS data yielded no significant differences between groups regarding bleaching sensitivity and gingival irritation. None of the teeth studied showed detectable enamel surface changes. Patient acceptance was statistically significantly higher in the tray group compared with the strip group (P .05). Conclusion: Both techniques demonstrated significant and comparable levels of tooth shade improvement after 2 weeks and 18 months. Each treatment caused similar, transient oral adverse effects. Keywords: follow-up, hydrogen peroxide, long-term stability, randomized clinical trial, shade relapse, tooth bleaching