Collegial relationships at work have become more important now that organizations increasingly use team-based work processes. Collegiality is also facing new challenges, however: more employees are meeting heavy demands beyond the workplace and making more frequent use of flexible work arrangements. This study seeks to explain the effect of employees' family demands on collegiality and evaluates whether the use of flexible work arrangements improves or impedes collegial behaviour. Moreover, we aim to investigate collegial behaviour as an exchange process between co-workers, and therefore also take family demands and the use of flexible work arrangements by co-workers into account as predictors of employee collegiality. Based on a sample of 1114 employees from 30 organizations, the results show that when used by the employee and co-workers, flexitime decreases collegiality. Collegiality is decreased when the employee has young children, but increased when co-workers have older children. The implications of these findings for HR practices are discussed.