The goal of this study was to compare drug and alcohol use, psychological symptoms and substance abuse treatment entry among 583 street-recruited, out-of-treatment injection drug users (IDUs) who used stimulants only, opiates only or both stimulant and opiate. Data analyzed from structured interviews indicated that stimulant-only users had the most severe alcohol problems and the highest psychological symptom scores for hostility, paranoia and psychoticism. In the 2 months following their interview only 3% of the stimulant-only users entered substance abuse treatment, as compared to nearly half of the participants in the other two groups. Even after controlling for variables that differed among the groups by logistic regression analysis, stimulant only users were still 24-25 times less likely than opiate only or both stimulant and opiate users to enter treatment. Researchers and clinicians are challenged to better understand and address the unique needs of stimulant users, including potential psychological problems and alcohol abuse, in order to attract them to treatment and serve them through a comprehensive treatment approach.