Nurses' perceptions of nursing error could affect their professional practice. The aim of the study was to explore critical care nurses' perceptions of nursing error and its causes. This was a qualitative study in which 12 critical care nurses were recruited through purposive sampling. The data were collected via in-depth interviews and analyzed through qualitative content analysis method (Elo & Kyngäs, 2008). Nursing error was deemed as an unavoidable issue which consisted of the lack of congruence with standards, doing extra-nursing tasks and giving care against the agreed-upon routines. Five categories emerged as the causes of error: individual reasons, work pressure, caring blindly, the uniqueness of caring environment and the lack of coordination among health care team members. The perception of nursing error is sort of unique; hence, managers should provide support for critical care nurses and pave the way for the prevention of errors.