The objective of this randomized, controlled, examiner-blind, parallel-group clinical study was to determine whether a tooth-whitening gel (Colgate Simply White Night Clear Whitening Gel) can significantly lighten teeth when used once daily at night, as compared with a commercially available dentifrice. Following a baseline tooth shade evaluation using the VITA Shade Guide, qualifying adult male and female subjects from the Buffalo, New York area were randomized into 2 treatment groups, which were balanced for baseline VITA Shade Guide scores, gender, and age. The treatment groups were: (1) a commercially available dentifrice only; and (2) a tooth-whitening gel in addition to a commercially available dentifrice. Subjects assigned to the 2 groups were given the dentifrice and a soft-bristled toothbrush. In addition, subjects in one of the groups were given the tooth-whitening gel. All subjects were instructed to brush their teeth for 1 minute twice daily (morning and evening) with the dentifrice. The subjects in the group also using the tooth-whitening gel were further instructed to apply the gel once daily at night, as per manufacturer instructions. Evaluations of tooth shade for each subject were repeated after 2 weeks, and again after 3 weeks of product use. In addition, evaluations of tooth shade for subjects using the tooth-whitening gel were later conducted at 6 months after product use. Seventy-five subjects complied with the protocol and completed the study. At the 2-week and 3-week examinations, subjects using the tooth-whitening gel and dentifrice exhibited statistically significant (P < .05) tooth shade lightening relative to baseline tooth shade. Furthermore, at the 2-week and 3-week examinations, subjects using the tooth-whitening gel exhibited statistically significant (P < .05) tooth shade lightening relative to subjects using only the dentifrice. In addition, the 6-month-postuse examination showed that subjects using the tooth-whitening gel exhibited statistically significant (P < .05) tooth shade lightening relative to baseline, thereby maintaining the tooth shade lightening that was evident at 3 weeks. The results of this clinical study indicate that after once-daily use at night for 2 or 3 weeks, the tooth-whitening gel provided statistically significant tooth shade lightening relative to baseline tooth shade for up to at least 6 months and also provided statistically significant tooth shade lightening relative to a commercially available dentifrice after 2 and 3 weeks of product use.