Abstract: Background Mental health problems often remain undetected and untreated. Prior research suggests that this is mainly due to a lack of need-perception and attitudinal barriers. The aim of this study is to examine unmet mental health needs using both a clinically assessed and a self-perceived approach in a Belgian province. Methods A cross-sectional survey study with a weighted representative sample of 1208 individuals aged 15 - 80 years old was carried out in 2021 in the province of Antwerp (Belgium). Mental health needs were defined as a positive symptom screening for depression (PHQ-9), anxiety (GAD-7) or alcohol abuse (AUDIT-C and CAGE), combined with experiencing significant dysfunction in daily life. Also 12-month health care use for mental health problems, self-perceived unmet mental health needs and reasons for not seeking (extra) help were assessed. Logistic regression analyses were used to explore the predictors of mental health problems, health care use, and objective and subjective unmet mental health needs. Results One in five participants had a positive screening on one of the scales, of whom half experienced dysfunction, leading to a prevalence of 10.4% mental health needs. Among those, only half used health care for their mental health, resulting in a population prevalence of 5.5% clinically assessed unmet mental health needs. Fourteen percent of the total sample perceived an unmet mental health need. However, more women and younger people perceived unmet needs, while clinically assessed unmet needs were higher among men and older people. One in six of the total sample used health care for their mental health, most of whom did not have a clinically assessed mental health need. Motivational reasons were most often endorsed for not seeking any help, while a financial barrier was the most important reason for not seeking extra help. Conclusions The prevalence of unmet mental health needs is high. Assessed and perceived (unmet) mental health needs are both relevant and complementary, but are ...