In this paper two contrasting methods of collecting data on drug injectors' needle and syringe sharing practices are considered, namely: direct questions about any previous sharing in the last 6 months, and vignettes in which injectors are asked to indicate whether they would be prepared to share injecting equipment in a range of situations. Injectors' statements of their preparedness to share are far in excess of their reports of actual sharing. The possible reasons for this discrepancy are considered, including that injectors may have under-reported the level of their actual sharing. It is suggested that in future studies aiming to collect risk behaviour data should seek to combine methods rather than to rely solely upon direct questioning of any past sharing.