Which disorder involves persistent worry that one is seriously ill despite medical reassurance?

The disorder characterized by persistent worry that one is seriously ill, despite receiving medical reassurance, is known as hypochondriacal disorder, often referred to as illness anxiety disorder. Individuals with this condition exhibit excessive concern about their health and may interpret normal bodily sensations as signs of severe illness. This preoccupation with fears about health causes significant distress and impairment, making it challenging for patients to feel reassured even after thorough medical evaluations.

In contrast, somatization disorder involves a pattern of multiple physical symptoms that cannot be fully explained by any underlying medical condition, yet the focus is more on the symptoms themselves rather than the fear of having a specific illness. Conversion disorder presents with neurological symptoms that are inconsistent with or cannot be fully explained by medical conditions, often arising as a psychological response to stress. Borderline personality disorder, while it can involve issues surrounding identity and relationships, does not specifically focus on the fear of having a serious illness.

Thus, hypochondriacal disorder is distinct in its emphasis on the anxiety surrounding one's health, aligning directly with the definition and symptoms presented.