The debriefing phase in human patient simulation is considered to be crucial for learning. To ensure good learning conditions, the use of small groups is recommended, which poses a major challenge when the student count is high. The use of large groups may provide an alternative for typical lecture-style education and contribute to a more frequently and repeated training which is considered to be important for achieving simulation competency. The purpose of the present study was to describe nursing students' experiences obtained during the debriefing conducted in small and large groups with the use of a qualitative descriptive approach. The informants had participated in a human patient simulation situation either in large or small groups. Data was collected through the use of five focus-group interviews and analysed by content analysis. The findings showed that independent of group-size the informants experienced the learning strategies to be unfamiliar and intrusive, and in the large groups to such an extent that learning was hampered. Debriefing was perceived as offering excellent opportunities for transferable learning, and activity, predictability and preparedness were deemed essential. Small groups provided the best learning conditions in that safety and security were ensured, but were perceived as providing limited challenges to accommodate professional requirements as a nurse. Simulation competency as a prerequisite for learning was shown not to be developed isolated in conjunction with simulation, but depends on a systematic effort to build a learning community in the programme in general. The faculty needs to support the students to be conscious and accustomed to learning as a heightened experience of learning out of their comfort zone.