Abstract The study aimed to explore the factors considered by medical doctors and legal experts when evaluating the need for legal guardianship in individuals with dementia, using a qualitative approach. In 2021–2022, medical doctors (N = 30) and legal experts (N = 20) from Finland underwent semi-structured individual interviews, addressing their perceptions of the need for guardianship in the Finnish context. Participants responded to pre-defined open-ended questions regarding how they assess this need and the factors influencing their conclusions. Thematic analysis of the audio-recorded and transcribed interviews revealed three main analytical groups: (i) prerequisites for appointing a guardian; (ii) factors expediting the need for a guardian; and (iii) factors delaying the need for a guardian. There are differences between professional groups in determining the need for guardianship. Some medical doctors may lack awareness of the legal requirements for guardianship or fail to consider them during assessments. To ensure proper assessment based on legal requirements, it is important for medical doctors to be aware of all legislation related to guardianship. Additionally, legal experts should have sufficient knowledge as regards cognitive and neuropsychiatric symptoms and their impact on mental capacity when assessing the need for guardianship. This research suggests that, in some cases, appointing a guardian is still considered necessary even though lighter support could suffice if available, or when no affairs need management.