Mental health care has moved from hospital settings to community mental health settings, and there is a need to explore the perceptions of patient safety among registered nurses working in this field. Patient safety is to include everyone and to be the goal in all aspects of health care. The aim of the study was to explore registered nurses’ perceptions of patient safety in community mental health settings for people with serious mental illness. The study was qualitative and descriptive in nature and interviews were carried out during spring 2012, with seven registered nurses working in community mental health settings for people with serious mental illness in five municipalities in the middle of Sweden. The sampling was purposive and data were analysed using qualitative content analysis. The findings showed that the registered nurses understood patient safety as providing support to people with serious mental illness in regaining and maintaining health through good treatment and respecting self-determination and avoiding coercion. The terms of daily living in small community mental health settings within the a large community health care organization, communication, sufficient knowledge of psychiatric disabilities among people in the residents’ network, and national laws and regulations, all had implications for patient safety. The registered nurses perceived patient safety as involving a wide range of issues that in other areas of care are more often discussed in terms of quality of care. Determining the boundaries of patient safety in community mental health settings for people with serious mental illness can be a first step in establishing workable routines that ensure safe patient care.