In what was otherwise an excellent article, Lawlor et al1 made no mention of a rare but important cause of delirium in cancer patients. Limbic encephalitis, a paraneoplastic syndrome of the central nervous system, is characterized by a subacute cognitive deterioration associated with severe impairment of recent memory and sometimes agitation, confusion, hallucinations, and seizures.2 In 80% of cases, the underlying primary malignancy is small-cell carcinoma of the lung, but it has also been described in a variety of other tumors, such as breast, ovary, uterus, testes, stomach, bladder, and kidney.3 Although reported to occur in approximately 3 per 1000 cancer patients, it is probably significantly underdiagnosed because of the difficulty in making the diagnosis.3 Anti-Hu antibodies are detected in the serum in about 50% of cases, but often the diagnosis is made at autopsy.3 Prognosis is poor, with the average survival measured in months from the time of onset, but there are anecdotal reports of a resolution of the condition with treatment of the tumor.4