Abstract Introduction Unwanted exposure (UE) to sexual content may have important consequences on children/adolescents’ psychosexual development. Our objective was to analyze UE to online pornography, parental filter use, type of sexual contents seen, emotional/behavioral reactions, and UE as positive/traumatic experience in Spanish adolescents and to examine these experiences and reactions depending on the type of sexual content. Methods In 2020, 500 Spanish teenagers (13–18 years) completed an ad hoc questionnaire for the evaluation of different dimensions involved in UE to sexual contents, such as those mentioned in the study objectives. Results A high frequency of UE (88.2%) is observed. Regarding the kind of scenes, naked people, straight porn, and people showing genitals are the most unexpectedly seen. Adolescents used to react to the UE closing the window and deleting sexual materials. A greater predominance of negative emotions was revealed, and another noteworthy result is related to the role played by type of sexual content and gender. Gay scenes and being woman increased the probability of living the experience as non-positive, and being woman and viewing naked people/BDSM scenes/under-age sex were associated with reactions of rejection. Conclusions This study contributes significantly to the knowledge of UE to online pornography in adolescents. It provides valuable information about the role played by the type of sexual content seen and the gender in the diverse reactions/experiences derived from the UE to pornography. Policy Implications This topic, that is, involuntary exposure to online sexual material in adolescents, should be included in affective-sexual education and prevention programs at early ages, so that children/adolescents are already trained in healthy sexuality when facing this type of content for the first time. These programs, adjusted to the reality of our adolescents, will minimize the negative impact that UE may have on their psychosexual development.