A sensation becomes a symptom (a concern) when a person associates it with potential illness. In the absence of objective evidence of a pathophysiological process that has important health consequences without treatment, assigning a diagnosis to the sensation is optional. This is important because labeling of benign bodily sensations as pathophysiology has potential advantages and disadvantages. We asked what patient and clinician factors are associated with willingness to accept an optional diagnosis. In a survey administered using Amazon M-Turk, 536 people anonymously completed validated measures for symptoms of anxiety and depression, intolerance of uncertainty, and skepticism regarding the healthcare system. They then viewed fictional personal medical scenarios in which they were asked to imagine they experienced certain symptoms, and were offered an optional diagnosis of a nerve problem, muscle pain syndrome, or fatigue syndrome, and were asked to rate their willingness to accept the diagnosis on an 12-point ordinal scale from 0 indicating "I do not accept it at all" to 11 indicating "I accept it with enthusiasm." The language of the scenarios was varied to attempt to reflect critical thinking, denigration of other doctors, an alternative mental health focus, or a hopeful outlook. Multilevel linear regression was used to identify factors associated with likelihood of accepting an optional diagnosis. Threshold likelihood of accepting an optional diagnosis greater than 5.5 on a 0 to 11 ordinal scale was independently associated with greater symptoms of anxiety (regression coefficient [RC]=0.38, 95% confidence interval [95% CI]=0.30-0.47, P <.001), greater skepticism regarding the healthcare system (RC=0.11, 95% CI=0.076-0.13, P <.001), and delivery tones characterized by either denigration of other doctors (RC=0.39, 95% CI=0.19-0.60, P <.001) or a hopeful outlook (RC=0.50, 95% CI=0.26-0.73, P <.001). Likelihood of accepting an optional diagnosis may be a sign of relative vulnerability from feelings of distress or distrust of medical evidence. Given this potential vulnerability, clinicians can take care to limit persuasive communication styles that can influence acceptance of optional diagnoses. III prognostic.