Worry, the cognitive enumeration and anticipation of potential future negative events, is associated with autonomic dysregulation, which may in turn have implications for the immune system. People endorsing high (n = 7) and normal levels of trait worry (n = 8) were briefly exposed to a phobic stimulus and the autonomic and immune responses and recovery were assessed. A time-matched control group (n = 6) was not exposed to any stimulus. Both worry groups showed increased heart rate and skin conductance in response to phobic fear. However, only the normal worry group showed a concomitant increase in natural killer cells in peripheral blood. Patterns of change during the follow-up period suggested that phobic fear had disrupted a normal circadian increase in natural killer cells. Adrenergic and hypothalamus-pituitary-adrenal mechanisms may be responsible for the differences between high and normal worry groups in their natural killer cell response to and recovery from phobic fear.