The architecture of sanatoria is changing due to the range of therapies, the development of therapeutic techniques or changing social needs. The aim of this study was to conduct an in-depth pre-design study to identify the specific functional-spatial needs of sanatorium users. To this end, an anonymous user needs survey was conducted using an online questionnaire. A total of 118 people were interviewed, defining not only the socio-demographic characteristics of the users, but also their functional-spatial needs. The survey included both open and closed questions, covering not only the functional scope of the designed facilities, but also specific equipment and access to green space. The results can be used as recommendations for architects and designers in the development of programmes for new buildings and for the modernisation, extension or adaptation of existing facilities. Participatory research with target users should be an important part of pre-project studies. The study was preceded by a brief and synthetic introduction including a historical overview of the sanatorium facilities. This is because their form and functional layout is often determined by the available technologies and forms of therapy.