The national study of Private Ownership of Firearms (NSPOF) was a nationally representative, random-digit-dial telephone survey. Interviews were conducted during November and December of 1994. A total of 2,568 interviews were completed out of 29,917 telephone numbers initially selected for the survey. Although the response rate was low, there is no reason to believe that the NSPOF involved a less representative sample than other telephone surveys that have been used to study DGU. Among 53 survey questions, each respondent was asked, "Within the past 12 months, have you yourself used a gun, even if it was not fired, to protect yourself or someone else, or for the protection of property at home, work, or elsewhere?" Respondents who answered "yes" to this question were then asked, "How many different times did you use a gun, even if it was not fired, to protect yourself or your property in the past 12 months?" Respondents who did not report a DGU during the past year were then asked, "Have you ever used a gun to defend yourself or someone else?" Respondents who had reported a DGU either in the past year or ever were asked, "Let's talk about the most recent incident. About how long ago was that?" The responses to this question allowed researchers to identify those gun uses that reportedly occurred within the past 5 years. Details of DGU incidents were supplied by respondents. The study found that estimates from this new survey are apparently subject to a large positive bias, which calls into question the accuracy of DGU estimates based on data from general-population surveys. Because DGU is a relatively rare event by any measure, a small proportion of respondents who falsely report a gun use can produce substantial overestimates of the prevalence of DGU, even if every true defensive gun user conceals his/her use. This analysis suggests that available survey data are not capable of determining whether reported DGU incidents, even if true, add to or detract from public health and safety. 5 tables and 30 references