Radioiodine treatment-induced hypothyroid psychosis is uncommon. Our literature search shows only three cases of hypothyroid psychosis developed within 3 months after the radioiodine treatment. Our case represents the first case of radioiodine-induced hypothyroidism presenting as psychosis much later (14 years) after the radioiodine treatment. A 60-year-old Chinese lady, with long-standing primary hypothyroidism due to the radioiodine treatment performed 14 years ago, presented with a 1-week history of hallucination, delusion and agitation. She was not on thyroid replacement. Thyroid function test done 14 years ago and again upon her admission to our facility was consistent with primary hypothyroidism. General blood tests and brain imaging were unremarkable. Her psychotic features resolved within 1 week with thyroid replacement and 9 days of antipsychotics. No further relapse of psychosis was noted. This emphasizes that radioiodine-induced hypothyroidism can go unnoticed for many years and present much later solely as psychosis.