OBJECTIVE: to evaluate the efficacy and chromatic stability after 4weeks, in all three thirds of the central incisor of two whitening treatments: in-office 37.5 % hydrogen peroxide (HP) treatment alone, and 37.5 % in-office HP followed by use of 6 % HP whitening strips (WS). METHODS: 60 participants were randomly divided into two groups of 30. Group 1 was treated solely with in-office 37.5 % HP. Group 2 followed the same in-office 37.5 % HP protocol, followed by WS over 2 weeks. The CIELAB colour were measured before and after every treatment stage. Colour differences were quantified and compared to the perceptibility thresholds. RESULTS: In-office 37.5 % HP treatment created a statistically significant increase in the L* coordinate and a statistically significant decrease in the a* and b* coordinates, resulting in perceptible colour changes in over 80 % of participants in all thirds of the tooth. In the group that used WS, the increase in L* and the decrease in a* and b* were maintained in the cervical and middle thirds after 4 weeks, whereas only the decrease in b* was maintained in the incisal third. In the group that did not use WS, the decrease in a* and b* was maintained in all thirds of the tooth after 4 weeks, but the increase in lightness was lost. CONCLUSIONS: The use of WS helped maintain that increase in lightness over 4 weeks. The decrease in the a* and b* coordinates caused by the 37.5 % HP treatment persisted after 4 weeks, whether WS were used or not. All the colour changes evaluated were perceptible in over 70 % of participants. CLINICAL SIGNIFICANCE: In-office treatment with 37.5 % HP increases lightness and decreases the quantity of yellow and red immediately but, if WS are not used, the impact on lightness is lost after 4 weeks. WS are a valid and effective treatment option in combination with in-office treatments to temporally extend the clinical treatment's whitening effect.