Most Finnish substance abuse therapists are women, while the majority of clients are men. This study explores the gender-based differences in the therapeutic alliance, retention in therapy and outcomes between female therapists (N = 30) and their clients (N = 296, women 101, men 195) in outpatient treatment. Female clients were more likely to want a female therapist, whereas men did not express such preferences. The clients' estimation of the therapeutic alliance differed at the first visit: female clients estimated it to be better than did men. The therapists' estimations were not connected to client's gender. The combination of a female therapist and a female client predicted a better therapeutic alliance during treatment, but there were no differences between male and female clients in long-term outcomes. The findings suggested that clients received treatment of the same quality regardless of their gender.