Worry about COVID-19 is a central topic of research into the social and economic consequences of the COVID-19 pandemic. Worry can be a negative and debilitating experience that damages mental health and discourages healthy re-engagement with the world, but it can also be a problem-solving activity, directing people’s attention to problems, and encouraging them to act accordingly. We present in this paper a way of measuring worry about catching COVID-19 that distinguishes between “functional fear” and “dysfunctional fear.” Drawing on work into fear of crime, our classification divides people into three groups: (1) the unworried, (2) the functionally worried (adaptive emotions encourage proactive behaviours to reduce the chance of infection) and (3) the dysfunctionally worried (quality of life is damaged by the emotional experience or taking ineffective or damaging precautions). Analysing data from two waves of a longitudinal panel study of over 1,000 individuals living in ten cities in England, Scotland and Wales, we find differing levels of negative anxiety, anger, loneliness, unhappiness and life satisfaction for each of the three groups, with dysfunctionally worried experiencing the most negative outcomes and functionally worried experiencing less negative outcomes than unworried. We find no difference between groups in compliance and willingness to re-engage in social life. Finally, we compare perceptions of risk (differentiating between likelihood, control and consequence) for each group, and find a difference between the dysfunctionally worried compared with functional and unworried groups. Our findings inform what sort of content-targeted messaging aimed at reducing dysfunctional worry might wish to promote. We conclude with some thoughts on the applicability of our measurement scheme for future research.