The belief that the full moon and disturbed behaviour are closely linked is alive and well, despite studies to the contrary. We investigated the possibility that there is an association between only extreme behavioural disturbance and the full moon.

We undertook an observational study of patients with violent and acute behavioural disturbance who presented to the emergency department of Calvary Mater Newcastle and patients with less severe behaviour for whom hospital security calls were made.

Proportion of patients for whom presentation or security call occurred in each lunar phase, modelled as a Poisson process.

Of 91 patients with violent and acute behavioural disturbance, 21 (23%) presented during the full moon — double the number for other lunar phases (P = 0.002). Sixty (66%) had either alcohol intoxication or psychostimulant toxicity, and five attacked staff (biting [2], spitting [1], kicking [1] and scratching [1]). In contrast, 512 hospital security calls for patients with less severe behaviour were evenly distributed throughout the lunar cycle.

Violent and acute behavioural disturbance manifested more commonly during the full moon.