Nowadays smartphones are used anywhere and at any time, day or night, by adolescents. Smartphone use, especially at night, is a risk factor for sleep disturbance and depression in adolescents. The purpose of this study was to analyse the correlation between smartphone use at night, sleep disturbance and depression symptoms in adolescents. This cross-sectional study analysed the data from 714 students in Surabaya, who were selected by using a simple random sampling technique. The independent variable was smartphone usage at night while the dependent variable was sleep disturbance and depressive symptoms. The data was collected using three questionnaires: the smartphone usage at night questionnaire, the Insomnia Severity Index questionnaire and the Kutcher Adolescent Depression Scale questionnaire. The data was then analysed using Spearman’s rho analysis (α < 0.05). The results indicated that there was a relationship between the use of smartphones at night and sleep disturbance in adolescents with a positive correlation (r = 0.374), and that there was a relationship between the use of smartphones at night and depression symptoms in adolescents with a positive correlation (r = 0.360). This study highlights that the excessive use of smartphones during the night may play a significant role in sleep problems and depressive symptoms among teenagers. Adolescents with sleep disturbance and depressive symptoms should be carefully monitored for signs of smartphone addiction. Nurses should improve health education for adolescents to inform them about the positive use of smartphones to prevent sleep disturbance and to minimise depressive symptoms.