Abstract: The invention relates to a portable psychological monitoring device, comprising an input, an output, a repository and a processor. The repository comprises a plurality of questionnaires, each comprising one or more questions relating to a mental state of a user. The processor is arranged for selecting a first questionnaire of the plurality of questionnaires, and presenting at least one of the questions of the first questionnaire to the user via the output at a first moment that is random to the user. The processor is arranged for receiving an answer to the question from the user via the input, and storing the answer into the repository. The invention further relates to a system for psychological monitoring, a method of assessment of a mental state of a user and a method of treatment or prevention of mood disorders and related disorder phenotypes.