This article assesses the impact of job insecurity on the mediating role of trust in the relationship between breach of the psychological contract and employee attitudes. It is argued that both objective and subjective job insecurity influence the relation between breach and trust, as well as the relation between breach and affective commitment, job satisfaction and intention to quit. Hypotheses for different configurations of subjective and objective job insecurity were tested in a sample of 834 Dutch workers employed in 48 organizations. In a multiple-group analysis, the relationships between breach, trust and employee attitudes in four groups of employees in different configurations of job security were analysed. The results show that objective job insecurity moderates the relationship between breach and trust. However, contrary to expectations, trust only partially mediates between breach and employee attitudes in all employment situations.