Prior studies of individuals with HIV infection have found that accessing psychiatric and substance abuse treatment when needed can improve health and prolong life, yet little is known about factors associated with treatment initiation. In a retrospective cohort design including individuals with HIV infection (?14 years old) in an integrated health care system in Northern California, this study included 822 patients with a major psychiatric diagnosis and 1,624 with a substance use disorder diagnosis. Data were extracted from a regional HIV registry and computerized databases. Twenty-four percent (N=198) of study patients with psychiatric diagnoses and 15% (N=245) with substance abuse or dependence received one or more specialty care visits within 12 months of diagnosis. Among patients with a psychiatric diagnosis, significant predictors of visiting a psychiatry clinic included not having an AIDS diagnosis at baseline or before the study (p=.049), having a diagnosis of major depression (p=.013), having a diagnosis of bipolar disorder (p<.001), and receiving a psychiatric diagnosis in 1996 versus later years of the study (p<.01). Among patients with a substance use disorder, significant predictors of initiating substance abuse treatment included age <30 (p=.015) and being in the HIV transmission risk group of injection drug use (p<.001). Clinical, diagnostic, and demographic factors were associated with specialty care treatment initiation in this sample of individuals with HIV infection and substance use or psychiatric disorders. Developing strategies to enhance treatment initiation has the potential to improve outcomes for individuals with HIV infection.