A dementia diagnosis is challenging to deliver and to hear, yet agreement about a diagnosis is essential for effective dementia care. We examined consensus about the results of a dementia evaluation in 90 patients assessed at an Alzheimer’s Disease Research Center. Diagnostic impressions were obtained from five sources: 1) the physician’s chart diagnosis, 2) the patient who was evaluated, 3) a companion present at the evaluation, 4) a diagnostic summary written by a nurse present during the evaluation, and 5) raters who watched a video of the diagnostic disclosure conversation. Overall, diagnostic consensus was only moderate. Patients and companions exhibited just fair agreement with one another. Agreement was better between physicians and companions compared to physicians and patients, though imperfect between the physician and video raters and the written summary. Agreement among sources varied by dementia severity, with lowest agreement occurring in instances of very mild dementia. This study documents discrepancies that can arise in diagnostic communication, which could influence adjustment to a dementia diagnosis and decisions regarding future planning and care.