The desirability or predicted value of a reward is influenced by the value of previously obtained rewards. Here, Richmond and colleagues reveal that in monkeys, the rhinal cortex — a component of the medial temporal lobe memory system — has an integral role in this contextual modulation of predicted value. Animals underwent a behavioural paradigm in which current reward value could only be predicted on the basis of the sizes of previously delivered rewards, which were varied across blocks of trials. Strikingly, despite this variation, monkeys with bilateral rhinal cortex lesions expected all forthcoming rewards to be of a similar size.