Background The classification of Alzheimer’s disease is undergoing a significant transformation. Researchers have created the category of “preclinical Alzheimer’s,” characterized by biomarker pathology rather than observable symptoms. Diagnosis and treatment at this stage could allow preventing Alzheimer’s cognitive decline. While many commentators have worried that persons given a preclinical Alzheimer’s label will be subject to stigma, little research exists to inform whether the stigma attached to the label of clinical Alzheimer’s will extend to a preclinical disorder that has the label of “Alzheimer’s” but lacks the symptoms or expected prognosis of the clinical form. Research questions The present study sought to correct this gap by examining the foundations of stigma directed at Alzheimer’s. It asked: do people form stigmatizing reactions to the label “Alzheimer’s disease” itself or to the condition’s observable impairments? How does the condition’s prognosis modify these reactions? Methods Data were collected through a web-based experiment with N = 789 adult members of the U.S. general population (median age = 49, interquartile range, 32–60, range = 18–90). Participants were randomized through a 3 × 3 design to read one of 9 vignettes depicting signs and symptoms of mild stage dementia that varied the disease label (“Alzheimer’s” vs. “traumatic brain injury” vs. no label) and prognosis (improve vs. static vs. worsen symptoms). Four stigma outcomes were assessed: discrimination, negative cognitive attributions, negative emotions, and social distance. Results The study found that the Alzheimer’s disease label was generally not associated with more stigmatizing reactions. In contrast, expecting the symptoms to get worse, regardless of which disease label those symptoms received, resulted in higher levels of perceived structural discrimination, higher pity, and greater social distance. Conclusion These findings suggest that stigma surrounding pre-clinical Alzheimer’s categories will depend highly on the expected prognosis attached to the label. They also highlight the need for models of Alzheimer’s-directed stigma that incorporate attributions about the condition’s mutability.