INTRODUCTION: Studies have found that increased mobile phone use (MPU) is associated with multiple health issues such as depression, disordered sleep and pain. However, the current situation and interrelationships of these problems remain unexplored in the Hong Kong population. OBJECTIVES: This study aimed to understand the situation and problematic use of mobile phones by Hong Kong secondary school students and to investigate depressive symptoms, bodily pain and daytime sleepiness and the associations of these factors with MPU in Hong Kong secondary school students. METHODS: This quantitative cross-sectional design study was based on self-administered questionnaires completed at five secondary schools. The questionnaire comprised five sections: MPU as measured by the Chinese version of the 10-Item Mobile Phone Problem Use Scale (CMPPUS-10); depressive symptoms according to the Depression Anxiety Stress Scale-21 Chinese Version (DASS-21); bodily pain according to the Brief Pain Inventory Short Form Chinese (BPISF-C); daytime sleepiness as measured using the Chinese version of the Epworth Sleepiness Scale (CESS) and socio-demographic questions. RESULTS: A total of 686 students were recruited. The CMPPUS-10 score correlated positively with the average daily duration of MPU and the presence of depression, daytime sleepiness and bodily pain. Problematic mobile phone users received significantly higher scores for depression severity, bodily pain and daytime sleepiness. Health problems were significantly more severe in female than in male students. Bodily pain and daytime sleepiness mediated the relationship of MPU with depression. CONCLUSIONS: Problematic MPU was associated with depression, bodily pain and daytime sleepiness. These findings will inform further studies of MPU-related health problems.