Background: Illicit drug use is an important public health problem. Identifying conditions that coexist with illicit drug use is necessary for planning health services. This study described the prevalence and factors associated with social and health problems among clients seeking treatment for illicit drug use. Methods: We carried out cross-sectional analyses of baseline data of 2526 clients who sought treatment for illicit drug use at Helsinki Deaconess Institute between 2001 and 2008. At the clients first visit, trained clinicians conducted face-to-face interviews using a structured questionnaire. Logistic regression was used to compute adjusted odds ratios (AORs) and 95 confidence intervals (CIs) for factors associated with social and health problems. Results: The mean age of the clients was 25 years, 21 (n = 519) were homeless, 54 (n = 1363) were unemployed and 7 (n = 183) had experienced threats of violence. Half of the clients (50 , n = 1258) were self-referred and 31 (n = 788) used opiates as their primary drugs of abuse. Hepatitis C (25 , n = 630) was more prevalent than other infectious diseases and depressive symptoms (59 , n = 1490) were the most prevalent psychological problems. Clients who were self-referred to treatment were most likely than others to report social problems (AOR = 1.86; 95 CI = 1.50-2.30) and psychological problems (AOR = 1.51; 95 CI = 1.23-1.85). Using opiates as primary drugs of abuse was the strongest factor associated with infectious diseases (AOR = 3.89; 95 CI = 1.32-11.46) and for reporting a combination of social and health problems (AOR = 3.24; 95 CI = 1.58-6.65). Conclusion: The existence of illicit drug use with other social and health problems could lead to increased utilisation and cost of healthcare services. Coexisting social and health problems may interfere with clients treatment response. Our findings support the call for integration of relevant social, medical and mental health support services within drug treatment programmes.