Background: This study sought to examine the occurrence of the problematic use of smartphones in a university sample and associated physical and mental health correlates, including potential relationships with risky sexual practices. Methods: A 156-item anonymous online survey was distributed via email to a sample of 9,449 university students. In addition to problematic smartphone usage, current use of alcohol and drugs, psychological and physical status, and academic performance were assessed. Results: A total of 3,425 participants were included in the analysis, of whom 20.1% reported problematic smartphone use. Problematic use of smartphones was associated with lower grade point averages and with alcohol use disorder symptoms. Problematic use of smartphones was also significantly associated with impulsivity (Barratt scale, ADHD), and elevated occurrence of PTSD, anxiety and depression. Finally, those with current problems with smartphone use were significantly more sexually active. Conclusion: Problematic use of smartphones is common, and has public health importance due to these demonstrable associations with alcohol use, certain mental health diagnoses (especially ADHD, anxiety, depression, and PTSD), and worse scholastic performance. Clinicians should enquire about excessive smartphone use as it may be associated with a range of mental health issues. Research is needed to address longitudinal associations.