BACKGROUND Data on mental health among injecting drug users in South Asia is scarce yet poor mental health among users has significant implications for the success of HIV prevention and treatment programmes. A cohort of 449 injecting drug users in Delhi was examined on the following issues (1) examine trends in suicidal ideation, suicide plan and suicidal attempts over a 12-month period, (2) examine association between injecting practices (receive and give used syringes) and suicidal ideation over a 12 month study period. METHODS An observational study was conducted providing phased interventions with follow up interviews every 3 months to 449 injecting drug users (IDUs), from August 2004 to November 2005. The study was conducted in Yamuna Bazaar, a known hub of drug peddling in Delhi. Interventions included nutrition, basic medical services, needle exchange, health education, HIV voluntary counseling and testing, STI diagnosis and treatment, oral buprenorphine substitution, and detoxification, each introduced sequentially. RESULTS Suicidal ideation and suicide attempts, did not significantly change over 12 months of observation, while suicide plans actually increased over the time period. Keeping other factors constant, IDUs with suicidal ideation reported more giving and receiving of used syringes in the recent past. CONCLUSIONS Mental health services are warranted within harm reduction programmes. Special attention must be paid to suicidal IDUs given their higher risk behaviours for acquiring HIV and other blood borne infections. IDU intervention programmes should assess and address suicide risk through brief screening and enhanced counseling.