Needle sharing is a risk factor for contracting blood-borne infections among injecting drug users (IDUs). We explored the relation of socio-financial, physical and mental health factors (ASI) to risk behaviour (Qr23) for contracting blood-borne infections among IDUs (Addiction Severity Index and Questionnaire for risk behaviour). 42 HIV negative IDUs were studied prospectively. The median age was 42.5 (range 18-61) y, 28 of 42 (67%) were males and median duration of injecting was 19.0 (range 0-43) y. HCV and HBV antibodies were found in 37 (88%) and 31 (71%) participants, respectively. Poly drug use was reported by 23 (55%) participants; amphetamine by 10 (24%) and heroin by 9 (21%). From the ASI data we were unable to find any statistically significant factor that was associated with needle sharing (n = 26/42, 61%) or sharing drug mixture/filter (n = 25/42, 59%). 19 (73%) of 26 participants who shared needles also shared drug mixture/filter. Of these 26 IDUs, 7 shared needles with partners, 11 with acquaintances, 3 with strangers and 5 with all categories. In conclusion, the study group showed differentiated risk behaviours for blood-borne infections with regard to various persons and to whom they were exposed. This suggests that IDUs may benefit from individualized counselling regarding risks for infections with HIV, HCV and HBV.