Self-esteem has not only been observed to be generally low in depression and anxiety, but also unstable. Few studies have looked at unstable self-esteem in clinical samples. The present study compared self-reported self-esteem instability across current depression (n = 60), anxiety (n = 111), and comorbid depression/anxiety (n = 71), remitted depression (n = 41), and anxiety (n = 29), recovered depression (n = 136) and anxiety (n = 98), and a never clinically depressed or anxious comparison group (n = 382). The comparison group had more stable self-esteem than all groups. Once controlling for overall levels of self-esteem, differences with current depression or anxiety, remitted depression, and recovered depression or anxiety remained, but disappeared for the comorbid group. The current findings are consistent with the view that not only enduring low self-esteem per se, but also high self-esteem reactivity may contribute to the aetiology of affective disorders.