This study examines multilevel relationships between perceived organizational support (POS), affective commitment and voluntary turnover among nurses. We explored the mediation role of affective commitment between POS and turnover behavior at both individual and work-unit levels. This cross-level study involved 945 Italian nurses from 60 work units. We hypothesized and showed that collective affective commitment fully mediated the impact of climate for POS on individual and collective turnover among nurses. This study helps explain the variance in turnover among nurses in healthcare organizations by analyzing the influence of unit-level climate on individual behavior. Results stress that social environments within wards are important in explaining the processes by which nurses decide to quit their work unit.