Evidence of reduced levels of needle sharing among injecting drug users (IDUs) has largely been confined to IDUs attending needle exchanges or receiving treatment. In this paper we present the results of a serial cross-sectional study of needle sharing conducted in Glasgow using a multisite sampling strategy. Of the estimated 9400 IDUs in the city, 503 were interviewed in 1990 and 535 in 1991. The proportion of IDUs reporting injecting with, or passing on used needles and syringes in the last 6 months fell significantly as did the number of individuals from whom equipment was received or passed on to. The impact of this level of sharing has been limited in terms of HIV transmission; the prevalence of HIV among the 1990 sample was 2.0% and 1.1% for the 1991 sample. However, the fact that third of IDUs in Glasgow continue to inject, even occasionally, with used equipment gives cause for concern in view of the other pathologies known to be associated with poor injecting hygiene.