The present study aimed to investigate the prevalence of Axis I disorders in adult inhalant-dependent patients in comparison to other substance-dependent patients and subjects without substance use disorders. The inhalant-dependent group consisted of 83 male inpatient and outpatient adults diagnosed according to DSM-IV criteria. This group was compared with 74 other substance-dependent patients and with 70 subjects without alcohol and substance use disorder diagnoses. Ninety-three percent of the inhalant dependents had a lifetime history of at least one type of comorbid Axis I disorder, while 77% of the same subjects had at least one type of any affective disorder and 75.9% of them had at least one type of anxiety disorder. Prevalence of Axis I disorders among inhalant dependents was 72.3% for lifetime major depression, 41% for major depression during the past month, 24% for dysthymic disorder, 20.5% for inhalant-induced depressive disorder, 27.7% for panic disorder, 30% for PTSD, 36.1% for social phobia and 20.5% for generalized anxiety disorder. The rate of lifetime axis I disorders was higher in patients with inhalant dependency in comparison to the other two groups. This finding suggests that inhalant-dependent adults have high rates of comorbid psychiatric problems, and that it is important to determine Axis I disorder comorbidity in this population before making an inpatient or outpatient treatment plan.