I describe a patient who developed a psychotic illness during the course of treatment for Graves’ thyrotoxicosis despite no history of psychiatric disease. Her psychotic symptoms appeared to be precipitated and later exacerbated by acute changes in her thyroid status. She required treatment with atypical antipsychotics along with in-patient psychiatric care before her symptoms were controlled. I believe that if thyrotoxic patients develop psychiatric symptoms during their treatment, this should be taken seriously and rapid changes in thyroid status should be avoided.