Thirty years into the HIV epidemic, we are still asking basic questions about how to measure the effectiveness of condom use. The importance of consistent condom use is strongly emphasised in health promotion literature, yet the evidence base for this is problematic—since reasons for condom use relate to perceived STI risk, and data are mostly retrospective in nature. Crosby et al1 report a prospective study using electronic daily diaries. The authors explored the relationship between both correct and consistent condom use, and STI acquisition, concluding that consistent use alone was not associated with STI rates, but consistent together with correct use was. The paper is interestingly discussed in an editorial by Ingham,2 who commends the prospective approach to measuring quality of …