Fear of crime is widely seen as an unqualified social ill, yet might some level of emotional response comprise a natural defence against crime? Our methodology differentiates between a dysfunctional worry that erodes quality of life and a functional worry that motivates vigilance and routine precaution. A London-based survey shows that one-quarter of those individuals who said they were worried about crime also viewed their worry as something akin to a problem-solving activity: they took precautions; these precautions that made them feel safer; and neither the precautions nor the worries reduced the quality of their lives. Fear of crime can therefore be helpful as well as harmful: some people are both able and willing to convert their concerns into constructive action. Tables and references (Published Abstract)