The study found an increased risk for near-repeat shootings within 2 weeks and one city block of previous shooting incidents. The risk for a near-repeat shooting was 33 percent greater than would be expected when no previous shooting occurred within a previous 2-week period within one block of a shooting incident. The researchers speculate that the reasons for near-repeat patterns in shootings are retaliation for the first shooting, a pattern of escalation in the use of firearms to commit crimes and advance criminal enterprises in a neighborhood, and the use of firearms to settle an ongoing dispute between neighborhood groups. It is possible that many of the near-repeat shootings result from complex events that require an understanding of the combined chain of events leading from one shooting to another before effective preventive measures can be designed and implemented. Study data were confirmed shootings in Philadelphia in which a victim was struck (aggravated assault) or killed (homicide) with a bullet or bullets. Data were obtained from the police record management system for the period of September 1, 2004, through September 30, 2005, and compared with the 13 prior months of August 1, 2003, through August 31, 2004. 1 table, 4 figures, and 41 references