Studies have suggested that cultural beliefs, such as those underlying religious social occasions and superstitions, have both positive and negative effects on mortality rates. Many people in Southern China believe that there are wandering ghosts who were released from hell during the lunar month of July (ghost month: mostly August in the Gregorian calendar): people therefore avoid unnecessary risky activities during ghost month. The aim of this study was to examine whether unintentional drowning deaths decreased during ghost month, using a matched control design and mortality data of Taiwan between 1981 and 2005. Results show that overall days-adjusted monthly death rate in ghost month days in Gregorian August was 1.37 (per 1,000,000). This was significantly lower than those in non-ghost month days, which was 1.67. The mean number of deaths in ghost months was lower than that in the matched controls, which was -3.2 deaths (-2.6 to -3.5) during weekends and -4.5 deaths (-2.2 to -7.2) during weekdays. The differences were more prominent in men than in women. For other main causes of death, we did not find persistent significant differences throughout the four matched controls. In conclusion, our findings support the death-dip hypothesis. Possible mechanisms are that people who believe in the ghost month might either decrease their exposure to water-related activities or involve themselves less in risky behaviours during ghost month, as a kind of risk compensation, consequently resulting in a reduction in the number of drowning deaths. As such we conclude that cultural factors should be taken into consideration when designing injury prevention programs.