Introduction: Unwanted mental intrusions (UMI) constitute the normal variants of obsessions in Obsessive-Compulsive Disorder (OCD), preoccupations about defects in Body Dysmorphic Disorder (BDD), images about illness in Hypochondriasis (HYP), and thoughts about eating in Eating Disorders (EDs). We sought to investigate the relationships between frequency and discomfort associated with the experience of the four UMI contents, adopting a within-subject perspective. Method: A group of 438 university students and community participants (Mage= 29.84, SD= 11.41; 70.54% women), completed the Questionnaire of Unpleasant Intrusive Thoughts to assess the frequency and discomfort of four UMI contents related to OCD, BDD, HYP and EDs. Results: Just over 76% of participants reported having experienced the four sets of intrusions. The ED-related were the most frequent but the least disturbing, whereas HYP intrusions were the least frequent but the most disturbing. The four UMI were significantly related to each other, both in frequency and discomfort. Women experienced OCD, BDD, and ED-related intrusions more frequently than men. Age was negatively associated with the frequency and distress of the four UMIs. Conclusions: UMIs might be a transdiagnostic variable across different disorders such as OCD, BDD, EDs, and Hypochondriasis, and they might contribute to explaining the phenomenological similarities among them.