Psychogeriatricians commonly undertake home visits, often under unusual and sometimes challenging circumstances. We report a home visit to a zoo to see an unusual case, a 49-year-old confused gorilla. A diagnosis of post-infarct delirium was made, subsequently validated by autopsy. We describe a primate observation scale which was used in the assessment of cognition this case, which may be helpful for use when cognitive assessment of primates is required.