Objective Longitudinal studies may help elucidate the factors associated with Problematic Internet Use (PIU); however, little prospective research has been conducted on the subject. The aim of the current study was to prospectively examine PIU in children/adolescents and identify the possible risk factors associated with transitions in PIU severity. Methods 650 middle-school boys were surveyed at two points one year apart and assessed for PIU using the Internet Addiction Proneness Scale for Youth (KS-II) and on other psychological characteristics. Results We found that 15.3% at baseline and 12.4% at one year met the criteria for at-risk/high-risk PIU (ARHRPIU). Both the persistent- ARHRPIU and emerging-ARHRPIU groups revealed greater depressive, motor impulsive, and smart-phone-addiction tendencies than the remitting-ARHRPIU group or the persistent low-risk group. In addition, we found that individuals exhibiting higher hyperkinetic attention-deficit/hyperactivity disorder (ADHD) scores were less likely to remit from ARHRPIU, and that individuals exhibiting more ADHD-related cognitive dysfunction and reporting fewer Internet-game-free days were more likely to demonstrate an emergence of ARHRPIU. Conclusion The present findings support previous studies in that specific negative-health features are linked to transitions in ARHRPIU. Furthermore, these findings suggest that intervention is needed and may be best targeted at specific groups of youths.