Successful technologies’ ubiquity changes uses, users and ethicolegal responsibilities and duties of care. We focus on dementia to review critically ethicolegal implications of increasing use of social networking sites (SNS) by those with compromised decision-making capacity, assessing concerned parties’ responsibilities. Although SNS contracts assume ongoing decision-making capacity, many users’ may be compromised or declining. Resulting ethicolegal issues include capacity to give informed consent to contracts, protection of online privacy including sharing and controlling data, data leaks between different digital platforms, and (...) management of digital identities and footprints. SNS uses in healthcare raise additional issues. Online materials acting as archives of ‘the self’ bolster present and future identities for users with compromised capacity. E-health involves actual and potential intersection of data gathered for the purpose of delivering health technological support with data used for social networking purposes. Ethicolegal guidance is limited on the implications of SNS usage in contexts where users have impaired/reduced capacity to understand and/or consent to sharing personal data about their health, medication or location. Vulnerable adults and family/carers face uncertainty in regard to consent, data protection, online identity and legal liabilities. Ethicolegal responsibilities and duties of care of technology providers, healthcare professionals, regulatory bodies and policymakers need clarification. (shrink)