The war in Afghanistan in 2001 may have had direct or indirect effects on drug users' behaviors in nearby Pakistan. We studied drug use patterns and correlates of needle sharing among injection drug users (IDUs) in Lahore, Pakistan, before and after the beginning of the Afghanistan war. Between August and October 2001, 244 drug users registering for needle exchange and other services underwent an interviewer-administered survey on sociodemographics, drug use and HIV/AIDS awareness. chi(2)-tests were used to compare drug use behaviors among subjects interviewed before and after October 6th, 2001, coinciding with the start of the Afghanistan war. Correlates of needle sharing among IDUs were identified using logistic regression. Comparing IDUs interviewed before and after October 6th, 2001, levels of needle sharing were significantly higher after the war (56% versus 76%, respectively; P=0.02). Factors independently associated with needle sharing included registering after the war began (adjusted odds ratio, AOR=3.76 (95% CI: 1.23-11.48)), being married (AOR=0.36), being homeless (AOR=3.91), having been arrested (AOR=6.00), and re-using syringes (AOR=6.19). Expansion of needle exchange, drug treatment and supportive services is urgently needed to avoid an explosive HIV epidemic in Pakistan.