We explored under-reporting of mental health symptoms and its correlates in adults receiving psychological treatment. We administered the Supernormality Scale (SS), the Minnesota Multiple Personality Inventory (MMPI-2-RF), the Narcissistic Personality Inventory (NPI), and the Beck Depression Inventory-II (BDI-2) to 147 patients at the start of their treatment. Supernormality (i.e., denial of common symptoms) was positively associated with MMPI faking good parameters supporting the construct validity of the SS. Furthemore, the correlation between supernormality and NPI was positive, albeit it modest (r = 0.20), indicating that patients high on grandiose/overt narcissism tend to deny common symptoms. The link between supernormality and depression symptoms as measured by the BDI was substantial and negative (r = -0.72). Our data suggest that patients with certain, to some extent overlapping traits – supernormality and narcissism – tend to under-report their depression symptoms. Given the clinical relevance of symptom under-reporting, our preliminary findings require a large-scale replication.