The aim of this research was to assess the psychological effects of the novel coronavirus disease (COVID-19) on mental health nurses. An internet-based questionnaire that included the Impact of Event Scale-Revised (IES-R) and the Zung Self Rating Anxiety Score (SAS) was used to assess the impact of the pandemic on the wellbeing of mental health nurses in an Irish mental health service. Among the nurses surveyed (n = 161), 12% of the participants had an overall IES-R score from 24 to 32 indicating that posttraumatic stress disorder (PTSD) was a clinical concern, while 38% had an overall IES-R score >32 indicating that PTSD was a probable diagnosis. The mean SAS score that had been converted to anxiety index scores was 40.78 (SD = 9.25). The results showed that 30% of mental health nurses experienced anxiety levels from moderate to extreme. Overall findings confirm that mental health nurses are experiencing psychological distress as a result of working during the COVID-19 pandemic. Nurses who were <30 years of age or who were in their current roles for less than a year or were ward-based and worked full-time, were most likely to be affected. Working during COVID-19 has not been routine work practice and for a cohort of workers who are already under pressure, the sacrifice in terms of general well-being has been immense. The offer of individualized psychological support for mental health nurses working during the pandemic should be both practical in nature and flexible enough to meet individual needs.