A 43-year-old man presented with an 18-month history of acute-onset cyclical behavioural change affecting mood, appetite, sleep, and energy levels. This had followed an initial episode of transient drowsiness which lasted 24 hours. On examination, there was some evidence of visual memory and frontal lobe deficits. A brain CT scan showed bilateral thalamic infarcts and a brain SPECT scan showed bilateral hypoperfusion of the frontal lobes. To our knowledge, this is the first reported case of thalamic infarction associated with acute-onset cyclical affective psychosis with clinical and neurophysiological features of frontal lobe syndrome. The case also highlights the possible role of thalamo-frontal circuits in the pathogenesis of the Kleine-Levin syndrome.