Epidemiological studies on problematic Internet use and problematic gaming conducted so far have mainly been carried out with unrepresentative and self-selected convenience samples, resulting in unreliable prevalence rates. This study estimates the prevalence of problematic Internet use and problematic gaming in a large sample of Spanish adolescents (N = 41,507) and identifies risk and protective factors for these risky behaviours. Data were collected online using the Adolescent Problem Internet Use Scale and the Adolescent Gaming Addiction Scale. Using a cut-off approach with measurement instruments inspired by the DSM-5 framework, we found a prevalence of 33% for problematic Internet use and 3.1% for problematic gaming. With a more conservative approach inspired by the ICD-11 framework, prevalence rates decreased to 2.98% for problematic Internet use and 1.8% for problematic gaming. Female gender, higher parents' education, elevated Internet connection time, reporting being online after midnight and using the mobile phone in class predicted problematic Internet use; whereas male gender, "living situation" where families do not have a traditional structure or stable environment, elevated Internet connection time and reporting using the mobile phone in class predicted problematic gaming. A cut-off approach involving scales that recycle substance use criteria (as in the DSM-5) over-pathologize Internet use and gaming behaviours. In contrast, the ICD-11 approach seems to provide more realistic and reliable prevalence rates.