Abstract Backgroud The objective is to compare the performance of the MHI-5 and GHQ-12, both measures of general mental health. Therefore, we studied the relationship of the GHQ-12 and MHI-5 with sociodemographic characteristics, self-reported visits to general practice and mental health care, and with diagnoses made by the general practitioner. Methods Data were used from the Second Dutch National Survey of General Practice, which was carried out in 104 practices. This study combines data from a representative sample of the Dutch population with data from general practice. Results The agreement between the GHQ-12 and MHI-5 is only moderate. Both instruments are however similarly associated with demographic characteristics (except age), self-reported health care use, and psychological and social diagnoses in general practice. Conclusions The performance of the MHI-5 and GHQ-12 in terms of predicting mental health problems and related help seeking behaviour is similar. An advantage of the MHI-5 is that it has been widely used, not only in surveys of mental health, but also in surveys of general health and quality of life, and it is shorter. A disadvantage of the MHI-5 is that there is no cut-off point. We recommend a study to establish a valid, internationally comparable cut-off point.