Abstract: OBJECTIVES. The sharing of contaminated injection equipment is the primary mode of human immunodeficiency virus (HIV) transmission for injection drug users. This study examined demographic factors, life events, and drug use practices that are potential risk factors for sharing injection equipment. METHODS. Between February 1988 and March 1989, 2921 active injection drug users were interviewed and questioned about their backgrounds, life-styles, and patterns of injection drug use. RESULTS. Of 2524 participants who reported injecting drugs within the 6 months prior to study enrollment, 70.4% reported recent needle sharing. A multivariate analysis found needle sharing to be more frequent among those with a history of arrest and lower socioeconomic status, even after accounting for other demographic and drug use variables. In addition, recent needle sharing was higher in male homosexual or bisexual men than in their heterosexual counterparts. CONCLUSIONS. These data suggest that injection drug users have an economic motive to share needles and that the availability of free and legal needles may reduce levels of needle sharing.