Despite the fact that the rate of substance abuse and dependence is higher among men than it is among women, the prevalence rates, especially the more recent ones, indicate that a diagnosis of substance abuse is not gender specific. From the emerging literature on gender differences over the past 25 years, male and female substance abusers are clearly not the same. Women typically begin using substances later than do men, are strongly influenced by spouses or boyfriends to use, report different reasons for maintaining the use of the substances, and enter treatment earlier in the course of their illnesses than do men. Importantly, women also have a significantly higher prevalence of comorbid psychiatric disorders, such as depression and anxiety, than do men, and these disorders typically predate the onset of substance-abuse problems. For women, substances such as alcohol may be used to self-medicate mood disturbances, whereas for men, this may not be true. Although these comorbid disorders might complicate treatment for women, women are, in fact, responsive to treatment and do as well as men in follow-up. Gender differences and similarities have significant treatment implications. This is especially true for the telescoping phenomenon, in which the window for intervention between progressive landmarks is shorter for women than for men. This is also true for the gender differences in physical and sexual abuse, as well as other psychiatric comorbidity that is evident in female substance abusers seeking treatment. The barriers to treatment for women are being addressed in many treatment settings to encourage more women to enter treatment, and family and couples therapy are standard therapeutic interventions. Negative consequences associated with substance abuse are different for men and women, and gender-sensitive rating instruments must be used to measure not only the severity of the problem but also to evaluate treatment efficacy. To determine whether gender differences observed over the past 25 years become less demarcated in comparisons of younger cohorts of substance abusers in the future will be interesting. Changing societal roles and attitudes toward women, the increase in women entering the workplace, in general, and into previously male-dominated sports and professions, in particular, may influence not only opportunities to drink but also drinking culture. Some gender differences likely will remain, but other gender differences will probably also emerge. The comparison of male and female substance abusers promises to be a fruitful one for researchers. The translation if the research findings to the treatment community to improve treatment outcome for both sexes will be an equally exciting challenge for the field.