<p>Online victimization has been linked to mental health problems. Youth often do not disclose these experiences, and little is known about disclosure barriers, particularly among youth with mental health challenges. This study aimed to fill this gap by identifying barriers to and facilitators of disclosure for this vulnerable group. Semi-structured interviews were conducted with 45 young people aged 13–22 from the UK and Norway who had mental health challenges and experiences with cyberbullying, sexual abuse online, and/or exposure to harmful content online. We asked the youth open-ended questions about digital activity and negative online experiences, whether they had disclosed such experiences, and what helped or stopped them from disclosing. The responses were analyzed using Reflective Thematic Analysis. Previous negative life experiences leading to lack of trust, being afraid of the consequences, and avoiding difficult feelings were described as barriers while disclosure was facilitated when they were asked directly about their online activities. Given the growing evidence for the association between mental health challenges and risky digital activities, more knowledge on disclosure barriers is needed. Since young people find it difficult to initiate conversations regarding events that they feel shameful for and fear negative consequences of disclosure, adults must actively inquire into online activities in a supportive and non-judgmental manner. Youth with mental health challenges may have had negative experiences in the past that caused them to lose trust. As a result, it is important to rebuild their trust. Disclosure is encouraged by asking direct questions about online activity.</p>