BACKGROUND: Mental health problems is frequent among children and psychopathology in early childhood seems to predict mental disorders in adulthood. All Danish children are offered seven free well-child visits at their General Practitioner (GP) during their first 5 years of life. GPs have a unique position to address mental health problems at the well-child visits, but they lack a systematic approach when assessing children's mental health. The purpose of this study was to investigate if the Strengths and Difficulties Questionnaire (SDQ) is a usable way to address preschool children's mental health in general practice. METHODS: A qualitative study of feasibility. Parents completed an online version of the SDQ at home. At the well-child visit, the GP used the SDQ results as a basis for a talk about the child's mental health. Afterwards the author JS conducted semistructured interviews with both the parent and the GP over the phone. The interviews were descriptively analyzed using the Framework Approach. RESULTS: Five primary care centres with 22 general practitioners in both Copenhagen and Region Zealand participated. Twenty four parents completed the SDQ and were interviewed. Participating parents and GPs agreed, that the SDQ introduced mental health as a natural and important part of the well-child visit. Online access had clear advantages: time for reflection at home and preparation, plus a clear result summary for the GP. Some of the GPs were worried that the questionnaire would be too time consuming, and might compromise the individualistic style of general practice. Some parents were worried if children with minor problems would be diagnosed. CONCLUSIONS: The online SDQ was well-accepted and feasible in daily practice. Implementing the SDQ into the well-child visit could strengthen the focus on the child's mental health. However, before the SDQ can be generally implemented a guideline on how to utilize it in the well-child visit is needed, as well as studies of efficacy in this setting. TRIAL REGISTRATION: Not relevant.