Background: Temporal patterns in the frequency and characteristics of self-harm episodes across the Australian asylum seeker population may have implications for self-harm prevention and public health policy. The aim of this study was to examine how the distribution of self-harm episodes and method(s) of self-harm used across the Australian asylum seeker population vary according to the 24-hour cycle, day, and month, and to establish a basis for further research., Methods and Findings: We conducted an observational study of all 949 self-harm incidents reported across the Australian asylum seeker population (representing a monthly average of 28,992 adults) between 1 August 2014 and 31 July 2015, obtained by Freedom of Information (FOI) from the Department of Immigration. Time of self-harm, day, and month of occurrence were investigated across all five Australian asylum seeker populations (i.e., community-based arrangements, community detention, onshore immigration detention, offshore immigration detention [Nauru], and offshore immigration detention [Manus Island]). Significant variations in distributions over the 24-hour cycle were observed by processing arrangements. Compared with the average distribution across all other processing arrangements, self-harm more commonly occurred among community-based asylum seekers (36.3%) between 12:00 AM and 3:59 AM (p < 0.001), in asylum seekers on Manus Island (36.4%) between 4:00 PM and 7:59 PM (p = 0.02), and among asylum seekers in onshore detention (20.4%) between 8:00 PM and 11:59 PM (p < 0.001). Compared with the average distribution across all other methods, self-poisoning (by medication) (25%) was significantly more likely to occur between 12:00 AM and 3:59 AM (p = 0.009), and self-battery (42%) between 8:00 AM and 11:59 AM (p < 0.001). The highest and lowest monthly self-harm episode rates for the whole asylum seeker population were in August (2014) (5 episodes per 1,000 asylum seekers; 95% confidence interval [CI] 1-11) and in both January and February (2015) (2.1 episodes per 1,000 asylum seekers; 95% CI 0.6-7.2), respectively; however, the overlapping CIs indicate no statistically significant differences across the months. When examining monthly trends by processing arrangements, we observed that self-harm was significantly more likely to occur in August (2014) than other months of the year among asylum seekers in onshore detention (19%) (p < 0.001), in January (2015) on Manus Island (18%) (p = 0.002), and in October (2014) on Nauru (15%) (p < 0.001). The main study limitations were that we could not investigate certain characteristics associated with self-harm (e.g., gender, country of origin), as the Department of Immigration did not routinely collect such data. There was also the potential risk of making a type 1 error, given the exploratory nature of the comparisons we undertook; we minimised this by lowering our significance threshold from 0.05 to 0.01., Conclusions: Self-harm in the Australian asylum seeker population was found to vary according to time of day and month of the year, by processing arrangements. A series of procedure-related and detention-related factors were observed to be associated with the temporal variations in self-harm. These findings should form the basis for further investigation into temporal variations in self-harm among asylum seekers, which may in turn lead to effective self-harm prevention strategies., Competing Interests: I have read the journal's policy and the authors of this manuscript have the following competing interests: KH is the founder of Community-Minded Psychological Services, a private practice for people from immigrant, asylum seeking, and refugee backgrounds in Melbourne, Australia, which has received funding from the Australian government to provide psychological support to asylum seekers. GC is employed at the Victorian Foundation for Survivors of Torture (Foundation House), an organization that receives funding from the Australian government to provide psychological assistance to asylum seekers, including those in immigration detention. KH was previously employed by the Victorian Foundation for Survivors of Torture. GC has been contracted by the Australian government’s Department of Home Affairs to provide training in relation to the psychological aspects of refugee status determination. KH has been contracted by the Australian government’s Department of Home Affairs to conduct independent mental health assessments and write psychological reports for the purposes of refugee status determination for asylum seekers who have been detained in offshore detention. This research was conducted in their personal capacity, however, and the views expressed here are their own, and those of their coauthors. RB and GA declare that they have no conflicts of interest.