BACKGROUND:Public awareness campaigns about depression and suicide have been viewed as highly effective strategies in preventing suicide, yet their effectiveness has not been established in previous studies. This study evaluates the effectiveness of a public-awareness campaign by comparing suicide counts before and after a city-wide campaign in Nagoya, Japan, where the city government distributed promotional materials that were aimed to stimulate public awareness of depression and promote care-seeking behavior during the period of 2010-2012. METHODS:In each of the sixteen wards of the city of Nagoya, we count the number of times that the promotional materials were distributed per month and then examine the association between the suicide counts and the frequency of distributions in the months following such distributions. We run a Poisson regression model that controls for the effects of ward-specific observed and unobserved heterogeneities and temporal shocks. FINDINGS:Our analysis indicates that more frequent distribution of the campaign material is associated with a decrease in the number of suicides in the subsequent months. The campaign was estimated to have been especially effective for the male residents of the city. LIMITATION:The underlying mechanism of how the campaign reduced suicides remains to be unclear. CONCLUSION:Public awareness campaigns can be an effective strategy in preventing suicide.